• 29.1 baseline — 0.6 × season 29.6 (14 gm) + 0.4 × last 10 28.4
• −1.0 opponent leak — they concede 333.3/game vs a 344.7 league average
• +1.7 at this ground — averages 30.9 there (55 gm)
• +0.9 wet forecast — averages 30.1 in the wet (12 gm)
• vs them: averages 28.3 over 10 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.