• 2.9 baseline — 0.6 × season 2.9 (9 gm) + 0.4 × last 10 2.9
• +0.2 opponent leak — they concede 101.3/game vs a 93.4 league average
• +1.0 at this ground — averages 3.9 there (21 gm)
• vs them: averages 4.7 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.