• 18.1 baseline — 0.6 × season 19.7 (7 gm) + 0.4 × last 10 15.7
• +0.3 opponent leak — they concede 375.7/game vs a 369 league average
• −3.9 at this ground — averages 14.2 there (9 gm)
• vs them: averages 10.0 over 1 game — evidence, never summed

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.