• 15.2 baseline — 0.6 × season 15.4 (14 gm) + 0.4 × last 10 14.9
• −0.4 opponent leak — they concede 335/game vs a 344.9 league average
• −1.2 at this ground — averages 14 there (27 gm)
• −0.4 wet forecast — averages 14.8 in the wet (15 gm)
• vs them: averages 16.0 over 5 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 9: 30 — far outside his usual range; kept in the average, not smoothed away.