Suggested number of groups in open card sorting

I'm going to use OptimalWorkshop for conduct an open card sorting exercises (unmoderated) with about 35 cards. I will recruit about 40 participants.

• Do I need to constrain the number of groupings while introducing the card sorting exercises?
• What is the recommended range?
• Or is it better to leave it as "group the information in the way and number you consider fit?"

For example, I imagine the responses may look very different if we tell a participant that they have to get it down to 2-4 groupings vs. 7-10 groupings.