• 4.5 baseline — 0.6 × season 4.5 (13 gm) + 0.4 × last 10 4.5
• −0.2 opponent leak — they concede 150.3/game vs a 155.4 league average
• +0.5 at this ground — averages 5 there (7 gm)
• vs them: averages 3.0 over 1 game — 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.