• 5.8 baseline — 0.6 × season 6.0 (20 gm) + 0.4 × last 10 5.4
• −0.6 opponent leak — they concede 51/game vs a 56.6 league average
• −0.2 at this ground — averages 5.6 there (14 gm)
• vs them: averages 4.5 over 10 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.