• 3.4 baseline — 0.6 × season 2.9 (17 gm) + 0.4 × last 10 4.1
• −0.6 opponent leak — they concede 28.9/game vs a 35.3 league average
• +2.6 at this ground — averages 6 there (4 gm)
• vs them: averages 3.0 over 4 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.