• 1.6 baseline — 0.6 × season 1.6 (15 gm) + 0.4 × last 10 1.7
• −0.1 opponent leak — they concede 54.9/game vs a 56.6 league average
• +0.5 at this ground — averages 2.1 there (19 gm)
• vs them: averages 1.7 over 6 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.