• 15.6 baseline — 0.6 × season 15.1 (13 gm) + 0.4 × last 10 16.5
• −1.1 opponent leak — they concede 343.2/game vs a 369 league average
• at this ground: too thin to count (3 gm) — shown, adds nothing
• vs them: averages 8.0 over 1 game — 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.