• 3.9 baseline — 0.6 × season 3.7 (6 gm) + 0.4 × last 10 4.3
• +0.1 opponent leak — they concede 160.7/game vs a 155.4 league average
• +0.7 at this ground — averages 4.6 there (15 gm)
• vs them: averages 8.0 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.