• 0.5 baseline — 0.6 × season 0.5 (21 gm) + 0.4 × last 10 0.5
• −0.1 opponent leak — they concede 8.1/game vs a 9.7 league average
• +0.1 at this ground — averages 0.6 there (10 gm)
• vs them: averages 0.0 over 1 game — 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.