I think I may know the answer to this and it's not great. I currently have the new lampeyes in a breeding box floating at the top of the tank. This is because I have an apisto. cacatuoides who made a meal of the last group of lampeyes I bought, as they were juveniles. The adults are too big for him to eat though. I thought I'd grow the new ones on a bit before letting them go, so they're in a breeding box with a moss ball, a new potted alternanthera reineckii that I bought at the same time, and a couple of stems of another new plant I bought floating at the top - not sure what that one is. I thought I'd use them as cover for the new lampeyes before planting them. They seem ok in there and are eating well, I don't think they'll need to be in there for much longer.
I can now see that there are definitely 5 males and 1 female there, bringing the total to 6 males and 4 females once they are released into the main tank. Unfortunately I have seen the males chasing each other about, especially at feeding time. I hope that this settles down a bit once they're in the main tank and have more space, although the only male currently in the tank has a bit of an attitude! I could go back to the LFS and ask for some more females, I have room for more I think, but that may be asking a bit much when they're so little in the shop tanks and are in a mixed sex group!