• 7.8 baseline — 0.6 × season 7.8 (20 gm) + 0.4 × last 10 7.6
• −0.4 opponent leak — they concede 201.8/game vs a 213.6 league average
• −1.3 at this ground — averages 6.5 there (20 gm)
• vs them: averages 3.5 over 2 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.