• 4.6 baseline — 0.6 × season 4.4 (15 gm) + 0.4 × last 10 4.8
• −0.6 opponent leak — they concede 80.8/game vs a 93.4 league average
• +0.2 at this ground — averages 4.8 there (4 gm)
• vs them: averages 2.0 over 3 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.