If you leave it just open it wouldn't do any trick compared to the closed one. For the audiable difference remove it with hinges together(I know it's pain to place it back when you need to keep it closed other times).
REGA 3- Sounds better with dust cover ON of OFF ?
Curious to hear comments regarding whether sound quality is impeded with dustcover open,closed OR removed? AND if felt mounted on the cover's edge to protect scrathes on the plinth has an averse affect?