• 1.3 baseline — 0.6 × season 1.3 (20 gm) + 0.4 × last 10 1.3
• −0.1 opponent leak — they concede 8.5/game vs a 9.4 league average
• −0.4 at this ground — averages 0.9 there (62 gm)
• vs them: averages 0.6 over 7 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.