• 54.3 baseline — 0.6 × season 55.3 (19 gm) + 0.4 × last 10 52.9
• +5.4 opponent leak — they concede 598.3/game vs a 544.2 league average
• −3.4 at this ground — averages 50.9 there (11 gm)
• vs them: averages 39.2 over 5 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.