• 4.6 baseline — 0.6 × season 4.6 (18 gm) + 0.4 × last 10 4.7
• +0.1 opponent leak — they concede 36.6/game vs a 35.7 league average
• +0.4 at this ground — averages 5 there (72 gm)
• vs them: averages 5.0 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.