• 1.6 baseline — 0.6 × season 1.6 (17 gm) + 0.4 × last 10 1.6
• −0.0 opponent leak — they concede 55.5/game vs a 56.6 league average
• −0.9 at this ground — averages 0.8 there (4 gm)
• vs them: averages 2.8 over 4 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.