• 6.2 baseline — 0.6 × season 6.2 (9 gm) + 0.4 × last 10 6.1
• −0.1 opponent leak — they concede 209.2/game vs a 213.6 league average
• +2.3 at this ground — averages 8.5 there (12 gm)
• +3.3 wet forecast — averages 9.5 in the wet (4 gm)
• vs them: averages 8.3 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.