• 4.6 baseline — 0.6 × season 4.6 (20 gm) + 0.4 × last 10 4.7
• +0.3 opponent leak — they concede 38.4/game vs a 35.7 league average
• −1.2 at this ground — averages 3.5 there (40 gm)
• vs them: averages 3.8 over 5 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.