• 1.1 baseline — 0.6 × season 1.3 (16 gm) + 0.4 × last 10 0.8
• −0.1 opponent leak — they concede 20.8/game vs a 23.6 league average
• −0.3 wet forecast — averages 0.8 in the wet (5 gm)
• vs them: averages 2.0 over 2 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.