• 17.0 baseline — 0.6 × season 17.7 (19 gm) + 0.4 × last 10 16.0
• −0.5 opponent leak — they concede 357.8/game vs a 369 league average
• at this ground: too thin to count (2 gm) — shown, adds nothing
• vs them: averages 19.4 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.