• 12.7 baseline — 0.6 × season 12.7 (10 gm) + 0.4 × last 10 12.7
• −0.0 opponent leak — they concede 544.7/game vs a 545.7 league average
• +2.8 at this ground — averages 15.5 there (20 gm)
• vs them: averages 12.3 over 4 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 22: 77 — far outside his usual range; kept in the average, not smoothed away.