• 12.2 baseline — 0.6 × season 12.3 (20 gm) + 0.4 × last 10 12.0
• −0.2 opponent leak — they concede 363.9/game vs a 369 league average
• −0.4 at this ground — averages 11.8 there (4 gm)
• −0.2 wet forecast — averages 11.9 in the wet (12 gm)
• vs them: averages 14.0 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 5: 21 — far outside his usual range; kept in the average, not smoothed away.