• 53.4 baseline — 0.6 × season 52.0 (20 gm) + 0.4 × last 10 55.4
• +1.5 opponent leak — they concede 559.8/game vs a 544.6 league average
• +8.7 at this ground — averages 62.1 there (60 gm)
• −3.0 wet forecast — averages 50.3 in the wet (15 gm)
• vs them: averages 66.6 over 12 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.