Yep, this is the single most important instruction and where I like others screwed up. You really can't insert the pick more that 4mm otherwise it risks going between the screen and the digitiser. There is almost no resistance so it is very easy to do. It is almost worth marking a 4 mm depth on each pick before starting. Getting the adhesive to lift was really easy it the screen is hot enough, sticking the pick in too far is also too easy :(

If you have the screen hot enough then it does lift and leave a small gap. I was really surprised. I was using the stronger suction cup that you can buy separately though

I used a heat gun from about 3 feet away with my hand right next to the iPad to gauge how hot it was. In the end you need the edge of the screen almost but not too hot to touch