• 5.1 baseline — 0.6 × season 5.1 (10 gm) + 0.4 × last 10 5.1
• −0.1 opponent leak — they concede 181.3/game vs a 185.9 league average
• +6.9 at this ground — averages 12 there (5 gm)
• vs them: averages 12.5 over 6 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.