• 3.7 baseline — 0.6 × season 3.6 (20 gm) + 0.4 × last 10 3.8
• −0.5 opponent leak — they concede 81.9/game vs a 93.4 league average
• −0.8 at this ground — averages 2.9 there (9 gm)
• vs them: averages 3.6 over 11 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.