• 1.8 baseline — 0.6 × season 1.9 (19 gm) + 0.4 × last 10 1.6
• +0.0 opponent leak — they concede 12.5/game vs a 12.2 league average
• +0.4 at this ground — averages 2.2 there (41 gm)
• vs them: averages 1.8 over 6 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.