• 6.1 baseline — 0.6 × season 6.2 (17 gm) + 0.4 × last 10 6.0
• +0.6 opponent leak — they concede 39/game vs a 35.7 league average
• +0.4 at this ground — averages 6.5 there (77 gm)
• vs them: averages 5.4 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.