• 12.5 baseline — 0.6 × season 12.2 (16 gm) + 0.4 × last 10 13.0
• +0.6 opponent leak — they concede 386.5/game vs a 369 league average
• −0.9 at this ground — averages 11.6 there (15 gm)
• vs them: averages 10.6 over 7 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 15: 20 — far outside his usual range; kept in the average, not smoothed away.