Hi Susan,
I care for lots of Ficus benjaminas that are kept indoors. I see you are in Zone 6b so you have to keep yours indoors in winter. These trees do usually drop lots of leaves whenever there is a significant change in light. That's why I often recommend finding a good, sunny indoor location for a Ficus and leaving it there year round. That spares the twice annual acclimatization process. Outdoors, the light is much more intense which encourages heavier growth. However, in your case, I'm not sure that is desirable as your tree is already too big.
Ficus trees respond very favorably to pruning at any time of the year. You really cannot go wrong in pruning a Ficus. Think of it as being like cutting hair. You can prune to any size or shape that you prefer. No matter how far back you prune, new growth will emerge just below each pruning cut and grow outward from there, So even if you prune back too far, you can be confident that it will fill out with a little time. I suggest that you be bold and experiment by pruning back more that you are initially inclined. Then watch how it grows back in and continue to prune to get it (and keep it) at the size and shape you prefer.
Pruning a Ficus tree is not so much a horticultural matter as an aesthetic one. Go for it!
http://garden.org/i/s/hurray.g...
I have written detailed articles on pruning indoor plants and caring for Ficus trees as indoor plants that I can email to anyone who requests them by email or posts an email address here.
~Will
