• 1.2 baseline — 0.6 × season 1.3 (18 gm) + 0.4 × last 10 1.0
• −0.0 opponent leak — they concede 9.3/game vs a 9.4 league average
• −0.5 at this ground — averages 0.7 there (48 gm)
• vs them: averages 0.8 over 5 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.