• 1.9 baseline — 0.6 × season 1.8 (18 gm) + 0.4 × last 10 1.9
• −0.2 opponent leak — they concede 28.6/game vs a 32.7 league average
• +0.6 at this ground — averages 2.5 there (4 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.