• 83.3 baseline — 0.6 × season 86.1 (18 gm) + 0.4 × last 10 79.0
• +1.4 opponent leak — they concede 1715.2/game vs a 1686.6 league average
• +6.9 at this ground — averages 90.2 there (5 gm)
• +54.2 wet forecast — averages 137.4 in the wet (7 gm)
• vs them: averages 98.2 over 9 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.