• 2.1 baseline — 0.6 × season 2.2 (13 gm) + 0.4 × last 10 1.9
• −0.1 opponent leak — they concede 31.4/game vs a 32.8 league average
• +2.1 at this ground — averages 4.2 there (6 gm)
• vs them: averages 2.5 over 10 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.