• 6.4 baseline — 0.6 × season 6.3 (20 gm) + 0.4 × last 10 6.6
• −0.6 opponent leak — they concede 141.4/game vs a 155.4 league average
• −2.5 at this ground — averages 3.9 there (73 gm)
• vs them: averages 3.6 over 9 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.