• 49.9 baseline — 0.6 × season 49.3 (20 gm) + 0.4 × last 10 50.9
• +4.6 opponent leak — they concede 594.5/game vs a 544.6 league average
• −10.7 at this ground — averages 39.2 there (14 gm)
• vs them: averages 33.5 over 11 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.