• 21.7 baseline — 0.6 × season 20.8 (18 gm) + 0.4 × last 10 23.0
• +0.1 opponent leak — they concede 546.2/game vs a 544.2 league average
• +5.8 at this ground — averages 27.5 there (6 gm)
• +14.2 wet forecast — averages 35.9 in the wet (7 gm)
• vs them: averages 27.0 over 10 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 19: 58 — far outside his usual range; kept in the average, not smoothed away.