• 23.2 baseline — 0.6 × season 22.9 (19 gm) + 0.4 × last 10 23.6
• −1.6 opponent leak — they concede 343.2/game vs a 369 league average
• −7.7 at this ground — averages 15.5 there (4 gm)
• vs them: averages 17.0 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.