• 15.8 baseline — 0.6 × season 15.0 (16 gm) + 0.4 × last 10 17.1
• +1.1 opponent leak — they concede 368.1/game vs a 344.7 league average
• +1.0 at this ground — averages 16.8 there (6 gm)
• vs them: averages 26.0 over 2 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.