• 23.1 baseline — 0.6 × season 23.4 (13 gm) + 0.4 × last 10 22.6
• −0.3 opponent leak — they concede 364.1/game vs a 369 league average
• −3.9 at this ground — averages 19.1 there (56 gm)
• vs them: averages 18.0 over 7 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.