• 38.4 baseline — 0.6 × season 36.3 (18 gm) + 0.4 × last 10 41.5
• +5.2 opponent leak — they concede 618.4/game vs a 544.2 league average
• −4.7 at this ground — averages 33.7 there (29 gm)
• vs them: averages 32.6 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.