• 1.3 baseline — 0.6 × season 1.3 (17 gm) + 0.4 × last 10 1.3
• −0.1 opponent leak — they concede 31.4/game vs a 32.7 league average
• −0.1 at this ground — averages 1.2 there (14 gm)
• vs them: averages 1.0 over 4 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.