• 5.4 baseline — 0.6 × season 5.0 (20 gm) + 0.4 × last 10 5.9
• +0.2 opponent leak — they concede 219.6/game vs a 213.6 league average
• −0.7 at this ground — averages 4.7 there (12 gm)
• vs them: averages 6.1 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.