• 14.6 baseline — 0.6 × season 15.7 (6 gm) + 0.4 × last 10 12.9
• +1.2 opponent leak — they concede 399.5/game vs a 369 league average
• −3.6 at this ground — averages 11 there (11 gm)
• vs them: averages 7.0 over 2 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.