My first thought is to place a gobo between the light and the overexposed tops of the bottles.
Saw Dean Collins do this with some jewelry, a watch to be exact. It was all exposed great except for the face of the watch, which was blown out. To solve it, he cut out a round piece of black paper and placed it on top of the tent (actually, he used a diffuser panel, per his usual lighting schemes, but fits what you're doing here) to essentially put a shadow only on the watch face in order to lower the exposure value of a specific part of the product.
Something to try.
Second thought is to feather the light so that it's less intense at the top and more at the bottom. Not sure if you can pull that off easily with a light tent. With a diffuser panel, you simply angle the light that hits the panel in such a way that the inverse square law works to your advantage; the panel area closer to the light source will be brighter, and you can use that to feather the light across your product.
In fact, that's probably what's going on here, but not to your advantage. If you've got lights on each side of the tent, and on on top, maybe just kill the one on top and see if that does the trick.