• 12.5 baseline — 0.6 × season 12.3 (15 gm) + 0.4 × last 10 12.8
• +0.0 opponent leak — they concede 213.7/game vs a 213.6 league average
• at this ground: too thin to count (1 gm) — shown, adds nothing
• −0.7 wet forecast — averages 11.8 in the wet (5 gm)
• vs them: averages 8.7 over 7 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.