I see them with some frequency. Female release of sex pheromone to attract a mate may draw in >1 male. I suspect that if males arrive at about the same time, it may lead to a bit of confusion until one gets the upper hand.

The pops fluctuate tremendously between & w/ years. Besides availability of nectar sources @ any given location, I think the winds and weather, along w/ the presence/absence of any nearly competing nectar sources combine to make numbers rise or fall. Day #s seem low 'cause some are unseen in trees?

I have done that for a couple of years. I make a count of adults active in my flowers and yard during the day and then go out after dark to count the monarchs I can find roosting in my trees. I typically find more roosting adults than I saw active at any one time.