• 17.9 baseline — 0.6 × season 17.8 (17 gm) + 0.4 × last 10 17.9
• +1.0 opponent leak — they concede 196.6/game vs a 185.9 league average
• −3.0 at this ground — averages 14.8 there (11 gm)
• vs them: averages 18.5 over 6 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: 26 — far outside his usual range; kept in the average, not smoothed away.