• 5.0 baseline — 0.6 × season 4.8 (17 gm) + 0.4 × last 10 5.4
• +0.4 opponent leak — they concede 60.8/game vs a 56.6 league average
• −0.2 at this ground — averages 4.8 there (77 gm)
• vs them: averages 4.3 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.