• 3.2 baseline — 0.6 × season 3.4 (14 gm) + 0.4 × last 10 2.9
• +0.2 opponent leak — they concede 34.8/game vs a 32.8 league average
• +2.1 at this ground — averages 5.3 there (4 gm)
• vs them: averages 5.0 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.