• 2.0 baseline — 0.6 × season 2.2 (15 gm) + 0.4 × last 10 1.8
• −0.1 opponent leak — they concede 11.8/game vs a 12.2 league average
• −0.3 at this ground — averages 1.8 there (37 gm)
• vs them: averages 2.2 over 5 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.