• 1.9 baseline — 0.6 × season 2.1 (17 gm) + 0.4 × last 10 1.6
• +0.0 opponent leak — they concede 57/game vs a 56.6 league average
• +1.3 at this ground — averages 3.3 there (4 gm)
• vs them: averages 2.8 over 10 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.