• 1.0 baseline — 0.6 × season 1.1 (19 gm) + 0.4 × last 10 0.8
• −0.0 opponent leak — they concede 22.4/game vs a 23.6 league average
• −0.2 at this ground — averages 0.8 there (41 gm)
• vs them: averages 0.8 over 5 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.