I use the so called 'professional' version called Shrink Links, invented by Mark Barrington about 14 years ago, so my experiece with that product may be different than the shrinkies that unlicensed people can buy online.

However, I have been using the product for years, and I'll give you my two cents worth:

1) I think most hair extension fusion wands get plenty hot enough to shrink the shrinkie.  An exception to that may be with the Doctored Locks shrinkies.  I have found their shrinking ability to be very inconsistent.  If you bought your shrinkies from shrinkies.net, I believe those are a much better quality and do shrink down quite well with a standard extension wand.

2) I do press down on the shrinkie with the wand.  I want the heat to really penetrate into the shrinkie.  Also, after it's heated and I remove the wand, I give the shrinkie a little squeeze with my fingers to make sure it will have a water tight seal.

3)I find that some shrinkies sizzle and some don't.  Not sure why.

4)I was taught to heat the shrinkies for no less than 8 seconds, to make sure it will adhere properly.  I usually heat them for 10 seconds just to be on the safe side!

Good luck!