I make through DT boxes and by no way an expert. If there is a dimensional rule of thumb I don't know of it. I make the box for something specific and make the box big enough for it.
Thanks for the reply.I have both the Incra and Leigh and have used both for dovetails. I recommend the Leigh. In my opinion, it's much more versatile and easier to set up..
I got a Leigh a year ago, love it, does take practice though.Looking for some good videos showing the setup and dialing in of the cuts......