• 14.9 baseline — 0.6 × season 16.3 (4 gm) + 0.4 × last 10 12.9
• +1.9 opponent leak — they concede 39.8/game vs a 35.3 league average
• −3.7 at this ground — averages 11.3 there (4 gm)
• vs them: averages 10.0 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.