• 1.8 baseline — 0.6 × season 1.8 (14 gm) + 0.4 × last 10 1.8
• +0.5 opponent leak — they concede 15.8/game vs a 12.2 league average
• +0.3 at this ground — averages 2.1 there (88 gm)
• vs them: averages 3.0 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.