• 2.1 baseline — 0.6 × season 2.1 (20 gm) + 0.4 × last 10 2.1
• +0.1 opponent leak — they concede 59.5/game vs a 56.6 league average
• +0.1 at this ground — averages 2.2 there (78 gm)
• vs them: averages 1.2 over 9 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.