• 2.5 baseline — 0.6 × season 2.5 (10 gm) + 0.4 × last 10 2.5
• −0.1 opponent leak — they concede 31.7/game vs a 32.7 league average
• −0.2 at this ground — averages 2.3 there (24 gm)
• vs them: averages 3.8 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.