• 1.2 baseline — 0.6 × season 1.2 (13 gm) + 0.4 × last 10 1.3
• −0.2 opponent leak — they concede 8.1/game vs a 9.7 league average
• +0.6 at this ground — averages 1.8 there (6 gm)
• vs them: averages 1.7 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 10: 5 — far outside his usual range; kept in the average, not smoothed away.