• 5.1 baseline — 0.6 × season 4.6 (19 gm) + 0.4 × last 10 5.7
• −0.5 opponent leak — they concede 141.4/game vs a 155.4 league average
• +0.5 at this ground — averages 5.6 there (67 gm)
• vs them: averages 3.0 over 7 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.