• 13.1 baseline — 0.6 × season 13.3 (17 gm) + 0.4 × last 10 12.7
• −0.7 opponent leak — they concede 175.7/game vs a 186.3 league average
• at this ground: too thin to count (2 gm) — shown, adds nothing
• vs them: averages 16.1 over 8 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.