• 23.9 baseline — 0.6 × season 24.0 (15 gm) + 0.4 × last 10 23.8
• −1.7 opponent leak — they concede 343.2/game vs a 369 league average
• +5.8 at this ground — averages 29.8 there (8 gm)
• vs them: averages 27.7 over 6 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.