• 4.2 baseline — 0.6 × season 4.2 (13 gm) + 0.4 × last 10 4.3
• −0.6 opponent leak — they concede 80.8/game vs a 93.4 league average
• −0.3 at this ground — averages 3.9 there (29 gm)
• vs them: averages 0.0 over 1 game — 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 21: 10 — far outside his usual range; kept in the average, not smoothed away.