• 4.2 baseline — 0.6 × season 4.3 (20 gm) + 0.4 × last 10 4.1
• −0.2 opponent leak — they concede 89.3/game vs a 93.4 league average
• −0.4 at this ground — averages 3.8 there (24 gm)
• vs them: averages 5.0 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.