• 23.1 baseline — 0.6 × season 22.7 (18 gm) + 0.4 × last 10 23.8
• +0.0 opponent leak — they concede 345.4/game vs a 344.7 league average
• +2.6 at this ground — averages 25.8 there (4 gm)
• +5.5 wet forecast — averages 28.6 in the wet (10 gm)
• vs them: averages 28.6 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.