• 15.7 baseline — 0.6 × season 15.7 (19 gm) + 0.4 × last 10 15.7
• −0.5 opponent leak — they concede 357.8/game vs a 369 league average
• −0.1 at this ground — averages 15.6 there (15 gm)
• vs them: averages 16.5 over 4 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.