• 4.2 baseline — 0.6 × season 4.0 (17 gm) + 0.4 × last 10 4.6
• +0.4 opponent leak — they concede 61.9/game vs a 56.6 league average
• −2.4 at this ground — averages 1.9 there (9 gm)
• vs them: averages 2.0 over 10 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.