• 8.6 baseline — 0.6 × season 8.4 (13 gm) + 0.4 × last 10 9.0
• −0.2 opponent leak — they concede 209.4/game vs a 213.6 league average
• +0.3 at this ground — averages 9 there (29 gm)
• vs them: averages 3.0 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.