• 2.1 baseline — 0.6 × season 1.7 (6 gm) + 0.4 × last 10 2.8
• +0.2 opponent leak — they concede 104/game vs a 93.4 league average
• +0.9 at this ground — averages 3.1 there (15 gm)
• vs them: averages 8.0 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.