• 13.5 baseline — 0.6 × season 13.4 (20 gm) + 0.4 × last 10 13.7
• +0.4 opponent leak — they concede 190.9/game vs a 185.9 league average
• at this ground: too thin to count (1 gm) — shown, adds nothing
• +1.2 wet forecast — averages 14.8 in the wet (8 gm)
• vs them: averages 11.1 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.