• 171.3 baseline — 0.6 × season 174.3 (16 gm) + 0.4 × last 10 167.0
• +0.8 opponent leak — they concede 1698.3/game vs a 1690.9 league average
• −32.1 wet forecast — averages 139.3 in the wet (8 gm)
• vs them: averages 160.3 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.