• 4.5 baseline — 0.6 × season 4.4 (19 gm) + 0.4 × last 10 4.7
• −0.1 opponent leak — they concede 55.5/game vs a 56.6 league average
• −1.1 at this ground — averages 3.4 there (54 gm)
• vs them: averages 2.8 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.