• 99.1 baseline — 0.6 × season 97.9 (17 gm) + 0.4 × last 10 100.9
• +1.7 opponent leak — they concede 1715.2/game vs a 1686.6 league average
• +38.7 at this ground — averages 137.8 there (6 gm)
• +0.7 wet forecast — averages 99.8 in the wet (8 gm)
• vs them: averages 142.6 over 10 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.