• 4.4 baseline — 0.6 × season 4.1 (19 gm) + 0.4 × last 10 4.8
• −0.3 opponent leak — they concede 322.1/game vs a 344.7 league average
• −1.2 at this ground — averages 3.1 there (8 gm)
• vs them: averages 2.0 over 4 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.