• 6.3 baseline — 0.6 × season 5.8 (20 gm) + 0.4 × last 10 6.9
• −0.4 opponent leak — they concede 87/game vs a 93.4 league average
• −0.5 at this ground — averages 5.8 there (19 gm)
• −1.1 wet forecast — averages 5.1 in the wet (8 gm)
• vs them: averages 4.7 over 11 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.