• 1.8 baseline — 0.6 × season 1.8 (16 gm) + 0.4 × last 10 1.8
• +0.2 opponent leak — they concede 64.3/game vs a 56.6 league average
• +0.1 at this ground — averages 1.9 there (15 gm)
• vs them: averages 2.1 over 7 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.