• 21.2 baseline — 0.6 × season 12.3 (4 gm) + 0.4 × last 10 34.7
• −1.4 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
• vs them: averages 46.3 over 3 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.