• 4.2 baseline — 0.6 × season 4.1 (17 gm) + 0.4 × last 10 4.4
• −0.1 opponent leak — they concede 54.9/game vs a 56.6 league average
• −0.5 at this ground — averages 3.7 there (46 gm)
• vs them: averages 3.6 over 5 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.