• 15.9 baseline — 0.6 × season 15.7 (19 gm) + 0.4 × last 10 16.1
• −1.1 opponent leak — they concede 343.2/game vs a 369 league average
• −3.3 at this ground — averages 12.6 there (54 gm)
• vs them: averages 10.6 over 5 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.