• 16.6 baseline — 0.6 × season 16.2 (20 gm) + 0.4 × last 10 17.1
• −0.2 opponent leak — they concede 364.1/game vs a 369 league average
• +1.2 at this ground — averages 17.8 there (5 gm)
• vs them: averages 19.0 over 1 game — 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.