• 2.7 baseline — 0.6 × season 2.6 (19 gm) + 0.4 × last 10 2.9
• +0.4 opponent leak — they concede 106.2/game vs a 93.4 league average
• −1.1 at this ground — averages 1.6 there (54 gm)
• −1.4 wet forecast — averages 1.3 in the wet (9 gm)
• vs them: averages 2.8 over 6 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.