• 27.2 baseline — 0.6 × season 25.8 (20 gm) + 0.4 × last 10 29.3
• −0.6 opponent leak — they concede 360.2/game vs a 369 league average
• −6.3 at this ground — averages 20.9 there (79 gm)
• vs them: averages 18.9 over 9 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.