• 1.3 baseline — 0.6 × season 1.2 (20 gm) + 0.4 × last 10 1.4
• −0.1 opponent leak — they concede 9.3/game vs a 9.7 league average
• −0.1 at this ground — averages 1.2 there (17 gm)
• vs them: averages 0.4 over 5 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.