• 2.9 baseline — 0.6 × season 2.9 (20 gm) + 0.4 × last 10 3.0
• +0.2 opponent leak — they concede 60.8/game vs a 56.6 league average
• +1.0 at this ground — averages 3.9 there (63 gm)
• vs them: averages 4.5 over 6 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.