• 11.9 baseline — 0.6 × season 11.9 (17 gm) + 0.4 × last 10 11.8
• −0.3 opponent leak — they concede 181.3/game vs a 185.9 league average
• +1.3 at this ground — averages 13.2 there (51 gm)
• vs them: averages 12.2 over 13 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: 3 — far outside his usual range; kept in the average, not smoothed away.