• 17.6 baseline — 0.6 × season 18.1 (15 gm) + 0.4 × last 10 16.8
• −0.2 opponent leak — they concede 363.9/game vs a 369 league average
• +1.0 at this ground — averages 18.6 there (79 gm)
• vs them: averages 18.7 over 14 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.