• 17.2 baseline — 0.6 × season 16.7 (18 gm) + 0.4 × last 10 17.8
• +0.0 opponent leak — they concede 369.9/game vs a 369 league average
• +3.8 at this ground — averages 21 there (6 gm)
• vs them: averages 23.0 over 8 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 3: 31 — far outside his usual range; kept in the average, not smoothed away.