• 4.1 baseline — 0.6 × season 3.8 (17 gm) + 0.4 × last 10 4.6
• −0.1 opponent leak — they concede 152.3/game vs a 155.4 league average
• +0.2 at this ground — averages 4.3 there (41 gm)
• vs them: averages 4.0 over 3 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.