If you're doing 3 light setups then I would suggest that you get a light meter.
You're just killing yourself doing it the way you are now.
Histograms are not as straight forward as you might think, especially when balancing multiple light sources.
Yes, you can guess and get it by using trial and error but that's time consuming and doesn't instill confidence in your clients when they see you fiddling around, taking test shots and making adjustments like that.
Using a light meter will eliminate all the guesswork, you'll be able balance your lights to each other and with ambient light, and you'll be able to repeat those settings anywhere, anytime.