• 20.2 baseline — 0.6 × season 20.5 (16 gm) + 0.4 × last 10 19.7
• +4.4 opponent leak — they concede 43/game vs a 35.3 league average
• +6.5 at this ground — averages 26.6 there (39 gm)
• vs them: averages 30.1 over 7 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 2: 43 — far outside his usual range; kept in the average, not smoothed away.