• 15.6 baseline — 0.6 × season 15.9 (17 gm) + 0.4 × last 10 15.1
• −0.2 opponent leak — they concede 364.1/game vs a 369 league average
• −3.2 at this ground — averages 12.3 there (6 gm)
• vs them: averages 11.0 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.