• 8.9 baseline — 0.6 × season 9.1 (19 gm) + 0.4 × last 10 8.7
• −0.5 opponent leak — they concede 175.7/game vs a 186.3 league average
• −1.4 at this ground — averages 7.5 there (4 gm)
• vs them: averages 8.0 over 5 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 23: 0 — far outside his usual range; kept in the average, not smoothed away.