• 3.2 baseline — 0.6 × season 3.2 (17 gm) + 0.4 × last 10 3.1
• −0.1 opponent leak — they concede 89.3/game vs a 93.4 league average
• +0.4 at this ground — averages 3.6 there (52 gm)
• vs them: averages 3.8 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.