• 20.2 baseline — 0.6 × season 19.4 (15 gm) + 0.4 × last 10 21.5
• −0.5 opponent leak — they concede 336.7/game vs a 344.7 league average
• at this ground: too thin to count (1 gm) — shown, adds nothing
• +4.3 wet forecast — averages 24.5 in the wet (6 gm)
• vs them: averages 27.8 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.