• 16.8 baseline — 0.6 × season 17.1 (14 gm) + 0.4 × last 10 16.4
• +0.4 opponent leak — they concede 377.9/game vs a 369 league average
• −1.0 at this ground — averages 15.8 there (25 gm)
• vs them: averages 14.3 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.