• 14.3 baseline — 0.6 × season 14.6 (17 gm) + 0.4 × last 10 13.8
• +0.4 opponent leak — they concede 559.8/game vs a 544.6 league average
• +3.5 at this ground — averages 17.8 there (31 gm)
• +5.1 wet forecast — averages 19.4 in the wet (11 gm)
• vs them: averages 17.4 over 5 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.