• 3.7 baseline — 0.6 × season 3.5 (19 gm) + 0.4 × last 10 3.9
• −0.1 opponent leak — they concede 55.5/game vs a 56.6 league average
• +0.7 at this ground — averages 4.4 there (13 gm)
• vs them: averages 4.0 over 10 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.