• 5.0 baseline — 0.6 × season 4.5 (15 gm) + 0.4 × last 10 5.6
• +0.7 opponent leak — they concede 106.2/game vs a 93.4 league average
• −2.0 at this ground — averages 3 there (19 gm)
• vs them: averages 5.2 over 6 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.