• 2.1 baseline — 0.6 × season 2.2 (13 gm) + 0.4 × last 10 1.9
• +0.0 opponent leak — they concede 33.5/game vs a 32.8 league average
• +0.4 at this ground — averages 2.5 there (37 gm)
• vs them: averages 4.8 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.