• 6.4 baseline — 0.6 × season 6.4 (9 gm) + 0.4 × last 10 6.3
• −0.7 opponent leak — they concede 31.2/game vs a 35.3 league average
• −2.3 at this ground — averages 4.1 there (9 gm)
• −4.4 wet forecast — averages 2 in the wet (4 gm)
• vs them: averages 2.6 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 1: 12 — far outside his usual range; kept in the average, not smoothed away.