Is your tobacco and solvent sealed inside a glass container (i.e a canning jar), during the heated extraction? I use half pint canning jars with matching lids/rings. I tighten the lid down "lightly" just like when canning in a hot water bath so that even though the jar is sealed any excess pressure buildup (like when I boiled the one extract), can still force its way past the lid seal. Close to it's boiling point, If the container isn't adequately sealed the hot ethanol can evaporate pretty fast.
After extraction, when separating the tobacco and solvent, how are you recovering solvent contained in the highly saturated tobacco? After the loose solvent has passed through the coffee filter, I gather the edges of the filter together encasing the saturated tobacco inside. I then gently squeeze the tobacco, gradually increasing pressure till I've recovered all the solvent I can without rupturing the filter. Saturated tobacco holds around 30 - 40% of the total solvent used, of that I'm able to recover perhaps 75%. In my case, what I don't/can't recover from the tobacco accounts for the majority of the overall loss.
That's really the only things I can think of.