• 102.8 baseline — 0.6 × season 105.8 (11 gm) + 0.4 × last 10 98.2
• −8.8 opponent leak — they concede 1543/game vs a 1687.8 league average
• −13.5 at this ground — averages 89.2 there (52 gm)
• vs them: averages 82.7 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.