Try using about 250 or 260, first. Iron temp for UltraKote is 230. UltraKote takes lower temps than MonoKote. If you start off at 300, you have effectively limited yourself to future shrink. At about 320 or so, UltraKote loses most of it shrink capability. Always use the lower temp you can so that in the future you can go a little higher and still have some shrink left. Using a heat gun start at about 250 or so and work just a little slower. Give it the opportunity to shrink. If at 250, you don't get any or enough, just raise the temp a little higher and try again.

Just my opinion, for what it's worth.