• 108.9 baseline — 0.6 × season 106.8 (13 gm) + 0.4 × last 10 111.9
• −1.5 opponent leak — they concede 1663.5/game vs a 1686.6 league average
• at this ground: too thin to count (3 gm) — shown, adds nothing
• vs them: averages 119.3 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.