• 54.0 baseline — 0.6 × season 53.4 (16 gm) + 0.4 × last 10 54.9
• −6.8 opponent leak — they concede 475.8/game vs a 544.2 league average
• at this ground: too thin to count (3 gm) — shown, adds nothing
• vs them: averages 41.2 over 5 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.