• 5.9 baseline — 0.6 × season 6.1 (20 gm) + 0.4 × last 10 5.7
• −0.4 opponent leak — they concede 145.2/game vs a 155.4 league average
• +0.6 at this ground — averages 6.5 there (42 gm)
• vs them: averages 4.8 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.