docs(flomni): document fermat_asymmetry's effective x/y spacing

Add an intuitive spacing table (x spacing stays at step, y spacing
becomes step/fermat_asymmetry) with a worked example, derived from
measuring actual generated positions (area-per-point vs. point count,
averaged over 20 randomized draws per ratio) rather than just stating
the formula. Mirrored into the OMNY port TODO so the same relationship
gets documented there once ported.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lx3KffiFyyDMKT8vvPENUW

csaxs_bec/bec_ipython_client/plugins/omny/AI_docs/TODO_fermat_asymmetry_port.md

@@ -13,6 +13,18 @@ symmetric, keeps x spacing fixed at `step` and scales y spacing by the ratio
 while preserving the requested FOV. Soft-clamped to `[0.1, 10]` (with a
 `logger.warning` when clamped), same style as `zshift`/`corridor_size`.
 
+**Effective spacing (verified against generated data, see
+`docs/plans/flomni-fermat-asymmetry.md`'s conversation for the measurement
+method):** x spacing always stays at `step`; y spacing becomes `step /
+fermat_asymmetry`. E.g. with `step=1 um`, `fovx=fovy=10 um`: `fermat_asymmetry=0.7`
+-> x spacing 1.0 um, y spacing ~1.43 um (sparser), ~70 points;
+`fermat_asymmetry=1.3` -> x spacing 1.0 um, y spacing ~0.77 um (denser),
+~130 points. Point count scales with the ratio since the FOV is fixed but
+the density isn't. Same relationship should be documented for OMNY once
+ported (Flomni's user doc has this table -- see
+`docs/user/ptychography/flomni.md`, "Effective spacing with
+`fermat_asymmetry`" -- OMNY's equivalent doc, if any, should get the same).
+
 ## Important: compose with the already-ported sub-step randomization
 
 Before this, `fixes/flomni_beamtime_2` already ported a *different* fix to

docs/user/ptychography/flomni.md

@@ -234,6 +234,18 @@ The basic scan function can be called by `scans.flomni_fermat_scan()` and offers
 Example:  
 `scans.flomni_fermat_scan(fovx=10, fovy=10, cenx=0, ceny=0, step=1, fermat_asymmetry=1.0, zshift=0, angle=0, exp_time=0.1, frames_per_trigger=1, burst_at_each_point=1)`
 
+**Effective spacing with `fermat_asymmetry`:** the x spacing always stays at `step`;
+the y spacing becomes `step / fermat_asymmetry`. So with `step=1 um`:
+
+| fermat_asymmetry | x spacing | y spacing | points (fovx=fovy=10 um example) |
+| --- | --- | --- | --- |
+| 0.7 | 1.0 um | ~1.43 um (sparser) | ~70 |
+| 1.0 (default) | 1.0 um | 1.0 um | ~100 |
+| 1.3 | 1.0 um | ~0.77 um (denser) | ~130 |
+
+The requested FOV stays exactly as specified either way -- only the point density
+(and therefore the point count and scan duration) changes.
+
 The Fermat spiral's sub-step phase is also randomized on every projection (drawn
 fresh per scan, not user-configurable) to decorrelate position-tied reconstruction
 errors that would otherwise accumulate into ring artifacts across a tomographic