• 2.2 baseline — 0.6 × season 2.1 (20 gm) + 0.4 × last 10 2.3
• −0.1 opponent leak — they concede 54.9/game vs a 56.6 league average
• +0.5 at this ground — averages 2.7 there (37 gm)
• vs them: averages 2.1 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.