• 1.4 baseline — 0.6 × season 1.3 (6 gm) + 0.4 × last 10 1.5
• −0.3 opponent leak — they concede 9.7/game vs a 12.2 league average
• +0.3 at this ground — averages 1.7 there (45 gm)
• vs them: averages 1.0 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.