• 0.6 baseline — 0.6 × season 0.6 (18 gm) + 0.4 × last 10 0.6
• −0.1 opponent leak — they concede 3.4/game vs a 4.2 league average
• −0.1 at this ground — averages 0.6 there (18 gm)
• vs them: averages 0.9 over 9 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.