• 22.7 baseline — 0.6 × season 23.3 (18 gm) + 0.4 × last 10 21.8
• −0.7 opponent leak — they concede 357.8/game vs a 369 league average
• −0.4 at this ground — averages 22.3 there (11 gm)
• +0.6 wet forecast — averages 23.3 in the wet (12 gm)
• vs them: averages 23.0 over 6 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.