I’m definitely not a professional, but i can speak from a lot of experience. You have an advantage over most of the professionals working on clients, as working on yourself gives you the ability to easily gauge the proper heat application and hopefully soon, the proper depth.
Admittedly, when i began doing it on myself i couldn’t properly internalize what i was doing wrong, to help me out with this i developed a trick. When i would destroy a sheath i would measure the length of the sheath against the needle and get the depth of insertion that way. Now this won’t work always because some of the follicles are deeper/shallower than others, i was just blessed with a massive amount of hair that was relatively the same depth.
Good luck!