• 52.4 baseline — 0.6 × season 51.8 (16 gm) + 0.4 × last 10 53.2
• +0.9 opponent leak — they concede 1715.2/game vs a 1686.6 league average
• −7.9 at this ground — averages 44.5 there (6 gm)
• −17.3 wet forecast — averages 35.1 in the wet (9 gm)
• vs them: averages 33.4 over 11 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.