• 4.2 baseline — 0.6 × season 4.0 (14 gm) + 0.4 × last 10 4.5
• −0.2 opponent leak — they concede 31.4/game vs a 32.7 league average
• −1.2 at this ground — averages 3 there (8 gm)

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.