• 14.7 baseline — 0.6 × season 14.7 (20 gm) + 0.4 × last 10 14.8
• +1.2 opponent leak — they concede 399.5/game vs a 369 league average
• +2.2 at this ground — averages 16.9 there (41 gm)
• vs them: averages 13.9 over 7 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.