• 4.7 baseline — 0.6 × season 4.7 (20 gm) + 0.4 × last 10 4.7
• +0.6 opponent leak — they concede 64.3/game vs a 56.6 league average
• −1.0 at this ground — averages 3.7 there (63 gm)
• vs them: averages 5.3 over 8 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.