• 11.5 baseline — 0.6 × season 11.5 (19 gm) + 0.4 × last 10 11.6
• −0.6 opponent leak — they concede 201.8/game vs a 213.6 league average
• −3.8 at this ground — averages 7.8 there (4 gm)
• vs them: averages 4.5 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.