• 15.1 baseline — 0.6 × season 15.4 (20 gm) + 0.4 × last 10 14.6
• −0.2 opponent leak — they concede 364.1/game vs a 369 league average
• +2.1 at this ground — averages 17.2 there (69 gm)
• vs them: averages 14.8 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 21: 1 — far outside his usual range; kept in the average, not smoothed away.