• 0.6 baseline — 0.6 × season 0.6 (11 gm) + 0.4 × last 10 0.6
• −0.0 opponent leak — they concede 4/game vs a 4.2 league average
• +0.2 at this ground — averages 0.9 there (28 gm)
• vs them: averages 1.5 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.