• 4.7 baseline — 0.6 × season 4.8 (20 gm) + 0.4 × last 10 4.6
• −0.0 opponent leak — they concede 35.6/game vs a 35.7 league average
• −2.8 at this ground — averages 1.9 there (30 gm)
• vs them: averages 4.5 over 4 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.