• 0.8 baseline — 0.6 × season 0.6 (17 gm) + 0.4 × last 10 1.0
• +0.0 opponent leak — they concede 12.8/game vs a 12.8 league average
• −0.3 at this ground — averages 0.5 there (38 gm)
• vs them: averages 2.0 over 1 game — 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.