• 20.7 baseline — 0.6 × season 20.7 (10 gm) + 0.4 × last 10 20.7
• −0.5 opponent leak — they concede 360.2/game vs a 369 league average
• +6.6 at this ground — averages 27.3 there (77 gm)
• vs them: averages 26.2 over 9 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 10: 31 — far outside his usual range; kept in the average, not smoothed away.