• 2.9 baseline — 0.6 × season 3.0 (20 gm) + 0.4 × last 10 2.8
• −0.1 opponent leak — they concede 181.6/game vs a 185.9 league average
• +0.8 at this ground — averages 3.7 there (27 gm)
• vs them: averages 5.0 over 4 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.