• 20.1 baseline — 0.6 × season 19.6 (12 gm) + 0.4 × last 10 20.8
• −0.1 opponent leak — they concede 185.2/game vs a 185.9 league average
• −4.6 at this ground — averages 15.5 there (4 gm)
• −5.6 wet forecast — averages 14.4 in the wet (7 gm)
• vs them: averages 15.6 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. Round 2: 9 — far outside his usual range; kept in the average, not smoothed away.