• 4.9 baseline — 0.6 × season 5.0 (20 gm) + 0.4 × last 10 4.7
• +0.0 opponent leak — they concede 345.7/game vs a 344.9 league average
• −0.7 at this ground — averages 4.1 there (8 gm)
• vs them: averages 5.9 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.