• 15.0 baseline — 0.6 × season 14.9 (19 gm) + 0.4 × last 10 15.1
• −0.4 opponent leak — they concede 180.6/game vs a 185.9 league average
• −0.7 at this ground — averages 14.3 there (37 gm)
• vs them: averages 15.3 over 7 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.