• 1.7 baseline — 0.6 × season 1.7 (20 gm) + 0.4 × last 10 1.7
• +0.3 opponent leak — they concede 14.9/game vs a 12.8 league average
• −0.2 at this ground — averages 1.5 there (51 gm)
• −0.1 wet forecast — averages 1.6 in the wet (8 gm)
• vs them: averages 2.0 over 5 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.