• 1.6 baseline — 0.6 × season 1.7 (6 gm) + 0.4 × last 10 1.6
• −0.5 opponent leak — they concede 8.8/game vs a 12.2 league average
• −0.8 at this ground — averages 0.9 there (7 gm)
• vs them: averages 0.3 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.