• 3.1 baseline — 0.6 × season 3.0 (13 gm) + 0.4 × last 10 3.2
• −0.3 opponent leak — they concede 32.7/game vs a 35.7 league average
• −1.2 at this ground — averages 1.8 there (56 gm)
• vs them: averages 1.3 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.