• 8.7 baseline — 0.6 × season 8.7 (9 gm) + 0.4 × last 9 8.7
• −0.5 opponent leak — they concede 200.8/game vs a 213.6 league average
• vs them: averages 6.0 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.