• 6.1 baseline — 0.6 × season 5.7 (19 gm) + 0.4 × last 10 6.7
• −0.3 opponent leak — they concede 148.3/game vs a 155.4 league average
• −2.8 at this ground — averages 3.3 there (12 gm)
• vs them: averages 3.3 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.