• 1.0 baseline — 0.6 × season 0.9 (16 gm) + 0.4 × last 10 1.0
• −0.1 opponent leak — they concede 3.9/game vs a 4.2 league average
• −0.1 at this ground — averages 0.9 there (19 gm)
• vs them: averages 0.7 over 3 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.