• 2.9 baseline — 0.6 × season 3.1 (19 gm) + 0.4 × last 10 2.7
• −0.3 opponent leak — they concede 10.8/game vs a 12.2 league average
• −0.4 at this ground — averages 2.5 there (28 gm)
• vs them: averages 2.0 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.