• 6.1 baseline — 0.6 × season 6.2 (20 gm) + 0.4 × last 10 5.9
• +0.4 opponent leak — they concede 166.4/game vs a 155.4 league average
• −0.3 at this ground — averages 5.8 there (18 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.