• 20.7 baseline — 0.6 × season 20.7 (10 gm) + 0.4 × last 10 20.7
• +1.1 opponent leak — they concede 389.2/game vs a 369 league average
• +7.0 at this ground — averages 27.7 there (15 gm)
• vs them: averages 29.4 over 10 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.