• 4.4 baseline — 0.6 × season 4.6 (19 gm) + 0.4 × last 10 4.0
• +0.0 opponent leak — they concede 155.9/game vs a 155.4 league average
• +0.4 at this ground — averages 4.8 there (16 gm)
• vs them: averages 5.3 over 3 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.