• 1.6 baseline — 0.6 × season 1.7 (20 gm) + 0.4 × last 10 1.5
• −0.2 opponent leak — they concede 50.6/game vs a 56.6 league average
• +0.9 at this ground — averages 2.5 there (31 gm)
• +2.5 wet forecast — averages 4.2 in the wet (6 gm)
• vs them: averages 3.7 over 3 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.