• 3.6 baseline — 0.6 × season 3.4 (19 gm) + 0.4 × last 10 3.9
• +0.9 opponent leak — they concede 117.8/game vs a 93.4 league average
• −0.5 at this ground — averages 3 there (31 gm)
• −0.9 wet forecast — averages 2.7 in the wet (6 gm)
• vs them: averages 3.0 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.