• 20.1 baseline — 0.6 × season 23.0 (4 gm) + 0.4 × last 10 15.8
• −1.3 opponent leak — they concede 1576.6/game vs a 1686.6 league average
• at this ground: too thin to count (1 gm) — shown, adds nothing

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.