• 6.1 baseline — 0.6 × season 6.3 (19 gm) + 0.4 × last 10 5.8
• −0.2 opponent leak — they concede 150.3/game vs a 155.4 league average
• −1.9 at this ground — averages 4.2 there (67 gm)
• vs them: averages 5.0 over 5 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.