• 2.8 baseline — 0.6 × season 2.9 (14 gm) + 0.4 × last 10 2.8
• +0.6 opponent leak — they concede 28.6/game vs a 23.7 league average
• −1.2 at this ground — averages 1.6 there (5 gm)
• vs them: averages 1.3 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.