• 13.6 baseline — 0.6 × season 13.5 (11 gm) + 0.4 × last 10 13.8
• +0.6 opponent leak — they concede 386.5/game vs a 369 league average
• +0.9 at this ground — averages 14.5 there (4 gm)

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.