• 7.7 baseline — 0.6 × season 7.8 (14 gm) + 0.4 × last 10 7.5
• +0.4 opponent leak — they concede 224.7/game vs a 213.6 league average
• +0.6 at this ground — averages 8.3 there (88 gm)
• +0.4 wet forecast — averages 8.1 in the wet (10 gm)
• vs them: averages 10.8 over 6 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.