• 1.6 baseline — 0.6 × season 1.5 (19 gm) + 0.4 × last 10 1.8
• −0.1 opponent leak — they concede 12.2/game vs a 12.8 league average
• −0.3 at this ground — averages 1.3 there (31 gm)
• vs them: averages 1.6 over 10 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.