• 15.5 baseline — 0.6 × season 16.2 (17 gm) + 0.4 × last 10 14.5
• +0.7 opponent leak — they concede 386.2/game vs a 369 league average
• −0.2 at this ground — averages 15.3 there (10 gm)
• vs them: averages 22.0 over 1 game — 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.