• 10.3 baseline — 0.6 × season 10.2 (20 gm) + 0.4 × last 10 10.5
• +0.5 opponent leak — they concede 386.5/game vs a 369 league average
• −0.8 at this ground — averages 9.4 there (67 gm)
• vs them: averages 8.8 over 9 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.