• 5.5 baseline — 0.6 × season 5.1 (20 gm) + 0.4 × last 10 6.2
• −0.6 opponent leak — they concede 82.5/game vs a 93.4 league average
• −1.9 at this ground — averages 3.6 there (70 gm)
• vs them: averages 2.8 over 12 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.