• 17.9 baseline — 0.6 × season 18.4 (16 gm) + 0.4 × last 10 17.2
• −1.0 opponent leak — they concede 514.9/game vs a 544.6 league average
• at this ground: too thin to count (1 gm) — shown, adds nothing
• +6.1 wet forecast — averages 24 in the wet (8 gm)
• vs them: averages 12.3 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.