• 1.0 baseline — 0.6 × season 0.9 (18 gm) + 0.4 × last 10 1.1
• −0.1 opponent leak — they concede 30.4/game vs a 32.7 league average
• +0.4 at this ground — averages 1.4 there (46 gm)
• vs them: averages 2.0 over 4 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.