• 26.3 baseline — 0.6 × season 26.6 (20 gm) + 0.4 × last 10 25.8
• +0.1 opponent leak — they concede 369.9/game vs a 369 league average
• −9.9 at this ground — averages 16.4 there (9 gm)
• vs them: averages 20.1 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.