• 8.3 baseline — 0.6 × season 8.1 (13 gm) + 0.4 × last 10 8.6
• +0.6 opponent leak — they concede 230.1/game vs a 213.6 league average
• +1.9 at this ground — averages 10.2 there (40 gm)
• vs them: averages 9.3 over 8 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. Round 20: 14 — far outside his usual range; kept in the average, not smoothed away.