Why is separating the screen proving to be so difficult?

I recently purchased a new battery and it's replacement tool kit from Ifixit to replace the battery in my Microsoft Surfsce Pro 4.

I was following the step-by-step instructions for replacing the battery, when I ran into my main challenge; rying to separate the screen from the main body of the device.

The step I was on involved using the iOpener heating pad to apply heat to the screens edge, in order to weaken the adhesive enough to gently pry it loose. The instructions were clear in that I should apply the iOpener to the screen edge in 2 minute increments. I might have to reapply it several times in order to get the screens edge warm enough to weaken the adhesive. But not soo warm as to damage the electronics underneath the glass or cause heat shock to the glass itself.

My problem is this: I've been unable to get the screen edge warm enough to weaken the adhesive. I have applied the iOpener heating paf in 2, 4, 6, 8, and 10 minute increments on separate attempts. Everytime, as soon as I remove the iOpener heating pad, the heat almost immediately bleeds away, and I'm left unable to wedge the provided tools underneath the edge of the glass.

I feel as if I'm not doing something correctly, but am unsure what that would be. Am I simply not applying enough heat? Where is he line between enough heat to weaken the adhesive and enough heat to damage the underlying electronics. I would greatly appreciate any insights and or advice into this matter, as this is the first time I have attempted this kind of repair. Thank you.