• 19.2 baseline — 0.6 × season 19.7 (17 gm) + 0.4 × last 10 18.5
• +0.5 opponent leak — they concede 377.9/game vs a 369 league average
• +2.1 at this ground — averages 21.3 there (32 gm)
• vs them: averages 22.4 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 19: 6 — far outside his usual range; kept in the average, not smoothed away.