• 12.0 baseline — 0.6 × season 12.1 (15 gm) + 0.4 × last 10 11.8
• −0.3 opponent leak — they concede 181.2/game vs a 185.9 league average
• +3.1 at this ground — averages 15.1 there (33 gm)
• vs them: averages 14.8 over 6 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 19: 5 — far outside his usual range; kept in the average, not smoothed away.