• 27.3 baseline — 0.6 × season 27.3 (10 gm) + 0.4 × last 10 27.3
• +0.8 opponent leak — they concede 559.8/game vs a 544.6 league average
• −14.5 at this ground — averages 12.8 there (10 gm)
• −19.9 wet forecast — averages 7.4 in the wet (5 gm)
• vs them: averages 14.7 over 3 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.