• 5.3 baseline — 0.6 × season 5.3 (10 gm) + 0.4 × last 10 5.3
• −0.6 opponent leak — they concede 50.3/game vs a 56.6 league average
• −0.7 at this ground — averages 4.6 there (50 gm)
• vs them: averages 5.7 over 9 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.