Yes but you need 5, so it's worth it to try 6.
The ADR system can be very weird that way. You are far less likely to find something for 2, so I wasn't saying to split your party into 2 people and 4 people, but rather to try 6 together even if 5 is what you need. There still might be nothing but as you continue to search, it's accessing a different pool of availability.