• 139.5 baseline — 0.6 × season 135.0 (21 gm) + 0.4 × last 10 146.2
• +2.4 opponent leak — they concede 1715.7/game vs a 1686.6 league average
• +12.4 at this ground — averages 151.9 there (61 gm)
• −9.4 wet forecast — averages 130.1 in the wet (16 gm)
• vs them: averages 159.4 over 13 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.