• 12.3 baseline — 0.6 × season 12.4 (9 gm) + 0.4 × last 10 12.0
• −0.2 opponent leak — they concede 363.9/game vs a 369 league average
• +1.4 at this ground — averages 13.6 there (16 gm)
• +1.3 wet forecast — averages 13.6 in the wet (5 gm)
• vs them: averages 13.5 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 18: 21 — far outside his usual range; kept in the average, not smoothed away.