From my humble point of view, if your lower floor attract lesser birds, you have some problem with the lower floor because bird tend to like lower floor cause the temperature is more stable and never too extreme.  Initial few nest maybe on the upper floor because it is brighter and feel safer due to new surrounding but gradually, they will go down to be safer as darkness is to their advantage. Yes, they play in the top floor and who doesn't, what fun to play in the dark unless you are playing hide and seek, Ha Ha Ha

Nine months ago, I have  a option to buy one of 2 BHs and one having 80+ nest on the lower floor and 10 on the upper floor and the other, having 4 in the lower floor and 50+ in the upper floor. I choose the one with 4 in the lower floor although the BH is the same price because I have the confidence that I will be able to make the lower floor better than the top floor when I solve the problem and the other BH is normal in to my belief.  Guess what, I am lucky,  after  6 months, I have 100+ in the upper floor and 600+ in the lower floor. Am I lucky, Am I lucky and I must be lucky.

Nothing to do with the lighting, maybe the entrance, temperature or humidity  or smell problem. Check them out and I maybe wrong and I am still learning to be better and better by trial and error and  to learn from you all each time I go on internet . Hopefully, those with good results will share their knowhows and experiences.

Lastly, me no sifu, just Swftlet ranger ana a lone ranger Ha Ha Ha