• 14.9 baseline — 0.6 × season 15.2 (19 gm) + 0.4 × last 10 14.6
• −1.7 opponent leak — they concede 31.2/game vs a 35.3 league average
• +3.1 at this ground — averages 18 there (30 gm)
• vs them: averages 17.4 over 7 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.