• 15.4 baseline — 0.6 × season 14.6 (16 gm) + 0.4 × last 10 16.5
• −0.2 opponent leak — they concede 363.9/game vs a 369 league average
• −3.9 at this ground — averages 11.5 there (10 gm)
• vs them: averages 11.7 over 6 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.