from 57.9 baseline, −2.2 at this ground

• 57.9 baseline — 0.6 × season 56.3 (20 gm) + 0.4 × last 10 60.3
• −2.1 opponent leak — they concede 523.4/game vs a 543.1 league average
• −2.2 at this ground — averages 53.9 there against the player's own 56.7 in those same seasons — 96% of that level (22 gm)
• vs them: averages 53.8 over 8 games — 103% of the player's own level in those seasons — evidence, never summed

Derived, not measured — plain arithmetic over 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. Round 11: 104 — far outside the usual range; kept in the average, not smoothed away.