• 14.1 baseline — 0.6 × season 15.1 (18 gm) + 0.4 × last 10 12.6
• −0.9 opponent leak — they concede 145.2/game vs a 155.4 league average
• −1.6 at this ground — averages 12.5 there (30 gm)
• vs them: averages 11.7 over 3 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.