• 22.5 baseline — 0.6 × season 21.9 (19 gm) + 0.4 × last 10 23.4
• −0.5 opponent leak — they concede 360.2/game vs a 369 league average
• −5.5 at this ground — averages 17 there (32 gm)
• vs them: averages 23.0 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.