• 14.9 baseline — 0.6 × season 14.9 (14 gm) + 0.4 × last 10 14.8
• −1.0 opponent leak — they concede 345.4/game vs a 369 league average
• +1.0 at this ground — averages 15.9 there (75 gm)
• vs them: averages 15.8 over 9 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.