• 4.2 baseline — 0.6 × season 4.7 (6 gm) + 0.4 × last 10 3.4
• +0.4 opponent leak — they concede 101.3/game vs a 93.4 league average
• −0.3 at this ground — averages 3.9 there (8 gm)
• vs them: averages 3.5 over 2 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.