• 73.0 baseline — 0.6 × season 91.9 (17 gm) + 0.4 × last 10 44.5
• −7.9 opponent leak — they concede 1504.1/game vs a 1687.8 league average
• +28.3 at this ground — averages 101.3 there (4 gm)
• vs them: averages 112.3 over 8 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.