• 20.5 baseline — 0.6 × season 20.0 (17 gm) + 0.4 × last 10 21.2
• −0.6 opponent leak — they concede 357.8/game vs a 369 league average
• −7.7 at this ground — averages 12.8 there (11 gm)
• vs them: averages 15.9 over 12 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.