• 0.5 baseline — 0.6 × season 0.4 (20 gm) + 0.4 × last 10 0.6
• −0.1 opponent leak — they concede 10.8/game vs a 12.2 league average
• −0.1 at this ground — averages 0.4 there (50 gm)
• vs them: averages 0.3 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.