• 16.7 baseline — 0.6 × season 16.8 (12 gm) + 0.4 × last 10 16.6
• +0.9 opponent leak — they concede 389.2/game vs a 369 league average
• +2.8 at this ground — averages 19.5 there (6 gm)
• vs them: averages 17.0 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.