• 2.8 baseline — 0.6 × season 3.1 (18 gm) + 0.4 × last 10 2.5
• +0.1 opponent leak — they concede 36.6/game vs a 35.7 league average
• +2.6 at this ground — averages 5.4 there (54 gm)
• vs them: averages 5.2 over 6 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.