• 27.8 baseline — 0.6 × season 28.3 (18 gm) + 0.4 × last 10 26.9
• −0.4 opponent leak — they concede 363.9/game vs a 369 league average
• −0.9 at this ground — averages 26.8 there (16 gm)
• +0.1 wet forecast — averages 27.9 in the wet (7 gm)
• vs them: averages 22.8 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.