• 12.3 baseline — 0.6 × season 13.0 (5 gm) + 0.4 × last 8 11.1
• −0.2 opponent leak — they concede 363.9/game vs a 369 league average
• at this ground: too thin to count (1 gm) — shown, adds nothing
• vs them: averages 12.0 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. Round 1: 3 — far outside his usual range; kept in the average, not smoothed away.