• 14.8 baseline — 0.6 × season 14.1 (16 gm) + 0.4 × last 10 15.7
• −1.0 opponent leak — they concede 507.7/game vs a 544.6 league average
• +4.3 at this ground — averages 19.1 there (23 gm)
• vs them: averages 27.2 over 6 games — evidence, never summed

Derived, not measured — plain arithmetic over his real games, shown in full. Adjustments can overlap (a game at this ground can also be a wet one); they add simply, and this note is the admission.