• 17.7 baseline — 0.6 × season 17.8 (13 gm) + 0.4 × last 10 17.7
• −0.5 opponent leak — they concede 357.8/game vs a 369 league average
• −1.1 at this ground — averages 16.7 there (29 gm)
• vs them: averages 17.0 over 2 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 7: 27 — far outside his usual range; kept in the average, not smoothed away.