• 15.0 baseline — 0.6 × season 15.3 (19 gm) + 0.4 × last 10 14.6
• −1.1 opponent leak — they concede 343.2/game vs a 369 league average
• −0.7 at this ground — averages 14.3 there (67 gm)
• vs them: averages 11.9 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.