• 20.8 baseline — 0.6 × season 20.9 (18 gm) + 0.4 × last 10 20.7
• +1.7 opponent leak — they concede 399.5/game vs a 369 league average
• at this ground: too thin to count (3 gm) — shown, adds nothing
• vs them: averages 17.0 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 11: 34 — far outside his usual range; kept in the average, not smoothed away.