• 2.7 baseline — 0.6 × season 2.6 (16 gm) + 0.4 × last 10 2.8
• +0.5 opponent leak — they concede 14.6/game vs a 12.2 league average
• −1.2 at this ground — averages 1.5 there (6 gm)
• vs them: averages 1.8 over 8 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.