• 13.3 baseline — 0.6 × season 12.6 (16 gm) + 0.4 × last 10 14.4
• −0.2 opponent leak — they concede 183.8/game vs a 186.3 league average
• +1.1 at this ground — averages 14.5 there (23 gm)
• vs them: averages 13.7 over 3 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.