• 4.9 baseline — 0.6 × season 4.5 (6 gm) + 0.4 × last 10 5.5
• −0.1 opponent leak — they concede 210.3/game vs a 213.6 league average
• +0.2 at this ground — averages 5.1 there (9 gm)
• vs them: averages 6.2 over 5 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.