• 17.4 baseline — 0.6 × season 17.8 (16 gm) + 0.4 × last 10 16.8
• +1.4 opponent leak — they concede 399.5/game vs a 369 league average
• −0.1 at this ground — averages 17.3 there (7 gm)
• vs them: averages 22.0 over 3 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.