• 3.8 baseline — 0.6 × season 4.3 (15 gm) + 0.4 × last 10 3.2
• −1.2 opponent leak — they concede 16.2/game vs a 23.7 league average
• −2.4 at this ground — averages 1.5 there (13 gm)
• vs them: averages 4.0 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.