• 2.1 baseline — 0.6 × season 2.1 (10 gm) + 0.4 × last 10 2.1
• −0.1 opponent leak — they concede 89.3/game vs a 93.4 league average
• −0.5 at this ground — averages 1.6 there (44 gm)
• vs them: averages 1.6 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.