• 15.3 baseline — 0.6 × season 14.5 (15 gm) + 0.4 × last 10 16.5
• −1.0 opponent leak — they concede 345.4/game vs a 369 league average
• +4.1 at this ground — averages 19.4 there (7 gm)
• vs them: averages 20.2 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 13: 30 — far outside his usual range; kept in the average, not smoothed away.