• 15.3 baseline — 0.6 × season 13.6 (19 gm) + 0.4 × last 10 17.8
• −0.4 opponent leak — they concede 335/game vs a 344.9 league average
• −1.9 at this ground — averages 13.4 there (13 gm)
• −11.1 wet forecast — averages 4.2 in the wet (6 gm)
• vs them: averages 5.8 over 9 games — evidence, never summed

Most signals here point under while you're on the over — worth reading the working above before you commit.

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.