• 3.4 baseline — 0.6 × season 3.4 (10 gm) + 0.4 × last 10 3.4
• +0.6 opponent leak — they concede 108.9/game vs a 93.4 league average
• +0.9 at this ground — averages 4.3 there (29 gm)
• vs them: averages 4.0 over 2 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.