• 169.7 baseline — 0.6 × season 167.0 (12 gm) + 0.4 × last 10 173.7
• +2.9 opponent leak — they concede 1715.2/game vs a 1686.6 league average
• +5.8 at this ground — averages 175.5 there (4 gm)
• −54.8 wet forecast — averages 114.9 in the wet (7 gm)
• vs them: averages 154.0 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.