• 16.4 baseline — 0.6 × season 16.3 (14 gm) + 0.4 × last 10 16.6
• +0.4 opponent leak — they concede 190.8/game vs a 185.9 league average
• −1.6 at this ground — averages 14.8 there (55 gm)
• −2.7 wet forecast — averages 13.8 in the wet (12 gm)
• vs them: averages 15.5 over 10 games — 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.