• 51.4 baseline — 0.6 × season 49.8 (14 gm) + 0.4 × last 10 53.8
• +4.9 opponent leak — they concede 597.6/game vs a 545.7 league average
• −12.9 at this ground — averages 38.5 there (56 gm)
• vs them: averages 56.0 over 1 game — 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.