• 33.4 baseline — 0.6 × season 33.4 (10 gm) + 0.4 × last 10 33.4
• −2.7 opponent leak — they concede 1550.3/game vs a 1687.8 league average
• −6.5 at this ground — averages 26.9 there (21 gm)
• vs them: averages 27.3 over 4 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.