• 6.2 baseline — 0.6 × season 6.3 (20 gm) + 0.4 × last 10 6.0
• −0.5 opponent leak — they concede 32.7/game vs a 35.7 league average
• −0.8 at this ground — averages 5.3 there (13 gm)
• vs them: averages 4.3 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.