• 5.4 baseline — 0.6 × season 5.4 (15 gm) + 0.4 × last 10 5.3
• +0.3 opponent leak — they concede 34.8/game vs a 32.8 league average
• −1.5 at this ground — averages 3.9 there (7 gm)
• vs them: averages 4.2 over 11 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.