I’m curious– if you want to recycle the bottles, why not cut off the bottom and grind the cut edges? Or fire polish them?
I’ve “recycled” glass in a number of different ways– creating frit and casting the glass, slumping the bottles into “flat” dishes, slumping bottles into a mold (really kind of interesting bowl), and other experiments that cost little. It doesn’t seem that your floral former idea will be a problem since you aren’t trying to stretch the glass to the point of creating holes or making the glass incredibly thin. Are you trying to widen the glass shape and thin out the glass? You might very well get a wavy edge depending on the thickness of the glass, gravity and the evenness of heat within the kiln.