• 2.8 baseline — 0.6 × season 2.7 (18 gm) + 0.4 × last 10 3.0
• +0.2 opponent leak — they concede 60.6/game vs a 56.6 league average
• −0.3 at this ground — averages 2.5 there (88 gm)
• vs them: averages 2.6 over 10 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.