Don't know why you want to glue them together. The way it's constructed, one thickness is able to slide on the other, which they really have to do when they are bent around the string. Now, on a split finger tab, you could cut off the ears that protect the inside of your fingers, because one or the other can sometimes lie flat and bunch up under the index or middle finger, but I rather like those as well. Not an issue on a three-under tab, of course.
I was a glove shooter for nearly 50 years, and still use a glove for hunting because it is quicker to put into action. However, I tried many tabs during that time and could never find anything that felt good to me. The Black Widow calf hair split finger tab is just the ticket. Except for hunting, that's all I shoot anymore.
Some folks do shorten all three layers of the tab, sometimes tapering, i.e., cutting each layer successively longer.