• 5.6 baseline — 0.6 × season 5.7 (9 gm) + 0.4 × last 10 5.5
• −0.4 opponent leak — they concede 87/game vs a 93.4 league average
• +0.4 at this ground — averages 6 there (16 gm)
• −2.6 wet forecast — averages 3 in the wet (5 gm)
• vs them: averages 5.8 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.