• 27.5 baseline — 0.6 × season 27.4 (8 gm) + 0.4 × last 10 27.8
• +2.3 opponent leak — they concede 399.5/game vs a 369 league average
• −6.1 at this ground — averages 21.4 there (15 gm)
• vs them: averages 24.5 over 8 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.