• 13.5 baseline — 0.6 × season 13.4 (19 gm) + 0.4 × last 10 13.6
• −0.3 opponent leak — they concede 209.2/game vs a 213.6 league average
• −2.5 at this ground — averages 11 there (12 gm)
• wet forecast: too thin to count (1 gm) — shown, adds nothing
• vs them: averages 11.3 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.