• 16.5 baseline — 0.6 × season 17.6 (16 gm) + 0.4 × last 10 14.9
• +0.8 opponent leak — they concede 386.5/game vs a 369 league average
• −1.6 at this ground — averages 15 there (39 gm)
• vs them: averages 14.7 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.