• 10.8 baseline — 0.6 × season 11.0 (5 gm) + 0.4 × last 10 10.6
• −0.5 opponent leak — they concede 353.4/game vs a 369 league average
• −1.0 at this ground — averages 9.9 there (7 gm)
• vs them: averages 8.0 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.