• 24.3 baseline — 0.6 × season 24.9 (20 gm) + 0.4 × last 10 23.4
• −4.2 opponent leak — they concede 29.3/game vs a 35.3 league average
• −12.7 at this ground — averages 11.6 there (30 gm)
• vs them: averages 13.0 over 4 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.