• 5.2 baseline — 0.6 × season 5.3 (12 gm) + 0.4 × last 10 4.9
• +1.4 opponent leak — they concede 117.8/game vs a 93.4 league average
• −0.7 at this ground — averages 4.5 there (58 gm)
• −1.7 wet forecast — averages 3.4 in the wet (14 gm)
• vs them: averages 4.9 over 8 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.