• 5.0 baseline — 0.6 × season 5.2 (20 gm) + 0.4 × last 10 4.8
• −0.6 opponent leak — they concede 82.5/game vs a 93.4 league average
• −0.3 at this ground — averages 4.8 there (32 gm)
• vs them: averages 4.7 over 9 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: 11 — far outside his usual range; kept in the average, not smoothed away.