• 4.5 baseline — 0.6 × season 4.2 (18 gm) + 0.4 × last 10 4.8
• −0.2 opponent leak — they concede 34.2/game vs a 35.7 league average
• −0.2 at this ground — averages 4.3 there (4 gm)
• vs them: averages 3.7 over 7 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.