• 14.9 baseline — 0.6 × season 14.6 (16 gm) + 0.4 × last 10 15.4
• +0.3 opponent leak — they concede 158.8/game vs a 155.4 league average
• −4.6 at this ground — averages 10.4 there (56 gm)
• vs them: averages 9.5 over 8 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.