• 3.8 baseline — 0.6 × season 3.5 (20 gm) + 0.4 × last 10 4.2
• +0.3 opponent leak — they concede 100.5/game vs a 93.4 league average
• +0.5 at this ground — averages 4.2 there (14 gm)
• vs them: averages 4.1 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.