• 3.8 baseline — 0.6 × season 4.0 (19 gm) + 0.4 × last 10 3.4
• +1.0 opponent leak — they concede 117.8/game vs a 93.4 league average
• +0.3 at this ground — averages 4.1 there (19 gm)
• −0.9 wet forecast — averages 2.9 in the wet (10 gm)
• vs them: averages 4.8 over 8 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.