• 20.5 baseline — 0.6 × season 21.8 (20 gm) + 0.4 × last 10 18.6
• −0.9 opponent leak — they concede 353.4/game vs a 369 league average
• +0.3 at this ground — averages 20.8 there (38 gm)
• vs them: averages 22.4 over 8 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.