• 5.4 baseline — 0.6 × season 5.4 (20 gm) + 0.4 × last 10 5.3
• −0.6 opponent leak — they concede 82.1/game vs a 93.4 league average
• +0.5 at this ground — averages 5.9 there (41 gm)
• vs them: averages 4.3 over 3 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.