• 39.1 baseline — 0.6 × season 38.8 (11 gm) + 0.4 × last 10 39.5
• −3.6 opponent leak — they concede 494.6/game vs a 544.2 league average
• at this ground: too thin to count (3 gm) — shown, adds nothing
• vs them: averages 38.8 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.