• 6.6 baseline — 0.6 × season 7.1 (18 gm) + 0.4 × last 10 6.0
• −0.9 opponent leak — they concede 80.8/game vs a 93.4 league average
• −2.0 at this ground — averages 4.6 there (11 gm)
• −0.7 wet forecast — averages 5.9 in the wet (12 gm)
• vs them: averages 7.3 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.