• 1.7 baseline — 0.6 × season 1.7 (14 gm) + 0.4 × last 10 1.6
• +0.1 opponent leak — they concede 25.8/game vs a 23.7 league average
• −0.3 at this ground — averages 1.3 there (6 gm)
• −1.1 wet forecast — averages 0.6 in the wet (7 gm)
• vs them: averages 1.8 over 9 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.