• 67.5 baseline — 0.6 × season 74.3 (19 gm) + 0.4 × last 10 57.3
• −0.9 opponent leak — they concede 1663.5/game vs a 1686.6 league average
• +21.7 at this ground — averages 89.3 there (4 gm)
• vs them: averages 94.8 over 6 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.