• 31.6 baseline — 0.6 × season 31.3 (20 gm) + 0.4 × last 10 32.1
• +1.5 opponent leak — they concede 386.5/game vs a 369 league average
• −1.7 at this ground — averages 29.9 there (40 gm)
• vs them: averages 28.0 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.