• 28.7 baseline — 0.6 × season 28.3 (20 gm) + 0.4 × last 10 29.2
• −0.4 opponent leak — they concede 363.9/game vs a 369 league average
• −2.0 at this ground — averages 26.7 there (36 gm)
• vs them: averages 26.7 over 6 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.