• 19.3 baseline — 0.6 × season 19.6 (19 gm) + 0.4 × last 10 18.8
• −0.3 opponent leak — they concede 363.9/game vs a 369 league average
• −4.8 at this ground — averages 14.5 there (8 gm)
• wet forecast: too thin to count (1 gm) — shown, adds nothing
• vs them: averages 13.6 over 5 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.