• 21.6 baseline — 0.6 × season 21.2 (20 gm) + 0.4 × last 10 22.2
• +0.1 opponent leak — they concede 369.9/game vs a 369 league average
• −4.7 at this ground — averages 16.9 there (43 gm)
• vs them: averages 18.4 over 7 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.