• 5.1 baseline — 0.6 × season 4.8 (6 gm) + 0.4 × last 10 5.6
• +0.3 opponent leak — they concede 164.6/game vs a 155.4 league average
• +4.1 at this ground — averages 9.2 there (5 gm)
• vs them: averages 8.1 over 7 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.