Offline replay of the L37 and L38 tube fields on the FI Style 2 helix shows no 7.8 m ripple from the tube distance itself (< 0.3 cm). The real signal is a step: the upper coil's 1 m fallback floor strip, composed independently, puts a support root 0.44 m from the lower bore's centreline at head height; the 7.8 m "period" is a sinusoid fitted to that step. Proposes pairing the floor cap with its bore. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1