• 31.3 baseline — 0.6 × season 30.0 (20 gm) + 0.4 × last 10 33.2
• +0.4 opponent leak — they concede 349.4/game vs a 344.7 league average
• −0.8 at this ground — averages 30.5 there (21 gm)
• vs them: averages 32.4 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.