• 12.7 baseline — 0.6 × season 13.2 (20 gm) + 0.4 × last 10 12.0
• +0.1 opponent leak — they concede 156.4/game vs a 155.4 league average
• −0.8 at this ground — averages 12 there (63 gm)
• vs them: averages 9.3 over 8 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 2: 21 — far outside his usual range; kept in the average, not smoothed away.