• 3.6 baseline — 0.6 × season 3.6 (11 gm) + 0.4 × last 10 3.6
• −1.3 opponent leak — they concede 15.1/game vs a 23.7 league average
• −2.6 at this ground — averages 1 there (4 gm)
• vs them: averages 0.0 over 3 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.