R6.2.3 — Chest-centric placement: +27 pp coverage gain for vital-signs cogs

Status: chest-vs-body placement benchmark · 2026-05-22

Premise

R6.1 showed the chest contributes 27.6% of CSI energy — 5× the per-limb value — and that limbs are confound, not signal for breathing-rate detection. R6.2 / R6.2.1 / R6.2.2 treated target zones as full body footprint (full bed, full chair, full standing zone). R6.2.3 asks: does targeting the chest specifically change the optimal placement?

If chest-centric and body-centric produce the same placement, the cog-time DSP work (limb masking in vital_signs.rs) suffices. If they differ, R6.2's CLI tool needs a --cog vital-signs flag that switches target-zone definitions.

Method

Same 5×5 m bedroom search as R6.2, but with two zone definitions:

Body-centric (R6.2 default):

bed: 1.5×0.5 → 3.5×2.0 m (3.00 m²)
chair: 3.5×3.5 → 4.3×4.3 m (0.64 m²)
desk: 0.2×2.5 → 1.2×3.1 m (0.60 m²)

Chest-centric (R6.2.3 new):

bed_chest: 60×40 cm patch where the chest sits while lying (2.2-2.8, 0.8-1.2)
chair_chest: 40×40 cm patch on the seat (3.7-4.1, 3.7-4.1)
desk_chest: 40×20 cm patch above the desk (0.5-0.9, 2.7-2.9)

Same antenna candidate grid, same greedy search.

Result

Configuration	Coverage	Best Tx	Best Rx	Link
Body-centric (R6.2)	49.3%	(4.25, 0)	(0, 3.25)	5.35 m
Chest-centric (R6.2.3)	82.4%	(2.0, 0)	(4.5, 5)	5.59 m

Cross-evaluation:

Apply to	Body-centric placement	Chest-centric placement
Body zones	49.3% (its own optimum)	40.3% (-9.0 pp)
Chest zones	55.5%	82.4% (+26.9 pp)

Chest-targeting wins by +26.9 pp on chest zones; body-targeting wins by +9.0 pp on body zones. The two strategies are not equivalent — chest-centric is a genuinely different deployment recipe.

Why the placement differs

The optimal placements:

Body-centric: corner-to-corner-ish (4.25, 0) → (0, 3.25). Threads across the room to cover bed + chair + desk by their gross-area centroids.
Chest-centric: diagonal (2.0, 0) → (4.5, 5). Threads through the 3 chest patches more efficiently because they are smaller + more clustered.

When target zones are small relative to the Fresnel envelope (40 cm at midpoint vs 40 cm chest zones), the Fresnel envelope can cover a chest entirely. When targets are large (3 m² bed), full coverage by a 40 cm envelope is impossible — the placement must compromise across the body's spatial extent.

Different geometry → different optimum.

Per-cog placement recommendation surfaced

R6.2.3 says R6.2's CLI tool should add a --target-mode flag:

`--target-mode`	Zone definition	Best cog use
`body` (default)	Full body footprint (current R6.2)	`cog-person-count`, `cog-pose-estimation`, `cog-presence`
`chest` (new)	40×40 cm chest patches	`cog-vital-signs`, `cog-breathing`, `cog-heart-rate`
`extremity` (future)	Hand / foot zones	Gesture detection cogs (out of scope for this loop)

The placement-search engine is unchanged; only the target zones differ. ~20 LOC change to the existing R6.2 CLI.

Composes with prior threads

R6.1 (multi-scatterer) — directly motivated this tick: chest = 27.6% of signal, limbs are confound.
R6.2 / R6.2.1 / R6.2.2 — orthogonal extensions: chest-centric works in 2D, 3D, and N-anchor; the principle is the same.
R14 V1 / V2 / V3 — V1 stress-responsive lighting + V3 attention-respecting both need breathing rate. Both should use --target-mode=chest at installation time. V2 HVAC uses presence + breathing → mixed mode (chest for breathing, body for presence). R6.2.3 says: configure the placement per cog deployed.
R12 PABS — chest-centric placement gives PABS better detection of body-near-bed scenarios (e.g. lying-down detection) because the chest envelope is dense at the expected chest location.

Honest scope

Chest position is approximated — humans don't sit / lie at fixed coordinates. In practice the chest zone should be slightly larger than 40×40 cm to absorb positional variance.
Per-cog zone schema is a deployment-time question, not a research one. The CLI option is the actionable output of this tick.
2D still — chest height (z=1.0-1.5 m for standing, 0.5-0.8 m for sitting, 0.2-0.4 m for lying) was implicit. A 3D chest-centric search (composing R6.2.1 + R6.2.3) would refine the placements further. Estimated +3-5 pp.
Single subject — multi-subject households have multiple chest centroids; the chest-centric optimum becomes the union of chest envelopes across expected occupant positions.

What this DOES enable

A clear cog-specific placement recipe: --target-mode=chest for vital-signs cogs.
Quantitative argument for adding the flag (+27 pp coverage is large enough to ship the CLI option).
Confirmation that R6.2's body-centric default is still right for most cogs — only vital-signs benefits from chest targeting.

What this DOES NOT enable

Multi-subject chest unions (out of scope for this tick).
3D chest-centric (R6.2.1 + R6.2.3 composition, future).
Pose-trajectory-aware chest zones — would need AETHER + R3 data to know where this household's specific subjects actually put their chests over time.

Next ticks

R6.2.3.1: 3D chest-centric placement (compose with R6.2.1).
R6.2.4: pose-trajectory-aware chest zone definition (AETHER-driven, needs ADR-105 federation to ship data-driven zones without raw transfer).
R6.2 CLI productisation: add --target-mode={body,chest} flag.

Connection back

R5 / R6 / R6.1 — physical basis; R6.1's chest dominance directly motivates this tick.
R6.2 / R6.2.1 / R6.2.2 — orthogonal extensions; R6.2.3 is a cog-mode option that composes with all three.
R14 (V1 lighting / V3 attention) — both should use chest mode.
R12 PABS — placement-driven detection sensitivity improves with chest-centric targeting for body-position-detection scenarios.
ADR-104 (ruview-mcp + ruview-cli) — --target-mode is a new CLI arg + a new MCP tool argument.