• 67.0 baseline — 0.6 × season 64.9 (18 gm) + 0.4 × last 10 70.2
• +5.0 opponent leak — they concede 1816.7/game vs a 1690.9 league average
• +11.1 at this ground — averages 78.1 there (9 gm)
• vs them: averages 63.6 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.