• 19.7 baseline — 0.6 × season 19.3 (20 gm) + 0.4 × last 10 20.2
• −1.3 opponent leak — they concede 345.4/game vs a 369 league average
• at this ground: too thin to count (3 gm) — shown, adds nothing
• vs them: averages 13.3 over 6 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.