• 6.1 baseline — 0.6 × season 6.1 (12 gm) + 0.4 × last 10 6.1
• −0.3 opponent leak — they concede 89.3/game vs a 93.4 league average
• −1.9 at this ground — averages 4.2 there (17 gm)
• vs them: averages 4.0 over 1 game — 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.