• 5.9 baseline — 0.6 × season 6.0 (20 gm) + 0.4 × last 10 5.8
• −0.3 opponent leak — they concede 34.1/game vs a 35.7 league average
• −2.2 at this ground — averages 3.8 there (4 gm)
• vs them: averages 6.7 over 3 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.