• 15.9 baseline — 0.6 × season 15.5 (13 gm) + 0.4 × last 10 16.6
• +0.4 opponent leak — they concede 378.4/game vs a 369 league average
• −0.1 at this ground — averages 15.9 there (65 gm)
• vs them: averages 17.0 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.