• 23.6 baseline — 0.6 × season 24.2 (18 gm) + 0.4 × last 10 22.7
• −1.5 opponent leak — they concede 345.4/game vs a 369 league average
• −4.1 at this ground — averages 19.5 there (30 gm)
• vs them: averages 19.7 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.