• 1.8 baseline — 0.6 × season 1.7 (11 gm) + 0.4 × last 10 1.8
• −0.2 opponent leak — they concede 10.8/game vs a 12.2 league average
• +0.4 at this ground — averages 2.2 there (84 gm)
• vs them: averages 1.6 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.