• 6.1 baseline — 0.6 × season 6.3 (15 gm) + 0.4 × last 10 5.9
• −0.3 opponent leak — they concede 89.3/game vs a 93.4 league average
• −0.7 at this ground — averages 5.4 there (80 gm)
• vs them: averages 5.1 over 8 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 15: 0 — far outside his usual range; kept in the average, not smoothed away.