• 42.8 baseline — 0.6 × season 40.3 (21 gm) + 0.4 × last 10 46.6
• +0.3 opponent leak — they concede 548.9/game vs a 544.6 league average
• −3.9 at this ground — averages 38.9 there (10 gm)
• vs them: averages 27.0 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.