• 0.5 baseline — 0.6 × season 0.6 (9 gm) + 0.4 × last 10 0.5
• −0.1 opponent leak — they concede 7.7/game vs a 9.4 league average
• −0.3 at this ground — averages 0.3 there (4 gm)
• +0.3 wet forecast — averages 0.8 in the wet (5 gm)
• vs them: averages 1.0 over 1 game — 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.