• 0.2 baseline — 0.6 × season 0.2 (18 gm) + 0.4 × last 10 0.1
• −0.0 opponent leak — they concede 4/game vs a 4.2 league average
• +0.1 at this ground — averages 0.3 there (10 gm)
• vs them: averages 0.5 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.