• 2.1 baseline — 0.6 × season 2.1 (12 gm) + 0.4 × last 10 2.1
• +0.4 opponent leak — they concede 14.9/game vs a 12.8 league average
• −0.4 at this ground — averages 1.7 there (72 gm)
• vs them: averages 2.4 over 5 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.