• 58.8 baseline — 0.6 × season 59.0 (20 gm) + 0.4 × last 10 58.5
• −7.4 opponent leak — they concede 475.8/game vs a 544.2 league average
• at this ground: too thin to count (2 gm) — shown, adds nothing
• vs them: averages 55.4 over 9 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.