• 5.3 baseline — 0.6 × season 5.3 (19 gm) + 0.4 × last 10 5.2
• −0.4 opponent leak — they concede 87/game vs a 93.4 league average
• −1.4 at this ground — averages 3.8 there (84 gm)
• vs them: averages 4.3 over 12 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.