• 15.5 baseline — 0.6 × season 14.6 (20 gm) + 0.4 × last 10 16.8
• +0.3 opponent leak — they concede 158.8/game vs a 155.4 league average
• −1.1 at this ground — averages 14.3 there (6 gm)
• vs them: averages 10.0 over 1 game — 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.