When you are stretching 5D-
BTC-BS (5 minutes Dynamic-Behind The Cheeks-Bundled Stretches) and attach at the base, during the set of 10 minutes you will elongate your tissue, and therefore you will be stretching your entire penis (inner and outer).
The key here is to relax fully into the stretch (reverse Kegel), and increase the intensity/stretching force during the set. I have explained this concept in the exercise, Penis Exterminator.
Imagine you're pulling a rope that is buried in the ground. In order to keep the intensity highest and be able to pull the rope out of the ground, you need to first pull the rope as close as you can to the ground, with time the rope will be pulled out and you need to get a new grip closest to the ground in order to keep the intensity high, and apply the highest pulling force on the rope in relation to the ground.
This above is an analogy what will happen with your penis/tissue.
This exercise will not work effectively, if you attach behind the glans when you start stretching. You will loose all the levarage and pulling force/intensity, when your tissue elongates during the set.
In the beginning when you are new to it, you can attach behind the glans but as you progress, you need to have the approach I'm explaining above. The limiting factor here is how hard you are willing to stretch.
This is the reason the stretching time for each set in this exercise is at 10 minutes. When you get to the highest intensity the stretching time = one set is 5 minutes. Rest and then go again for 5 minutes.
If you can go longer time you are not stretching hard enough. When you get to the maximum intensity, you will be able to get a temporary stretched flaccid stretch increase of ~2 cm (0.79 Inch).
Trust me. If you begin all your stretching sessions in indefinitely by attaching behind the glans there is no way you can produce maximum temporary elongation after a session.
I hope I explained this well.