• 20.0 baseline — 0.6 × season 19.9 (14 gm) + 0.4 × last 10 20.1
• −1.3 opponent leak — they concede 322.7/game vs a 344.9 league average
• +2.3 at this ground — averages 22.3 there (44 gm)
• vs them: averages 13.0 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.