I’ve done two HIMs and doing a 3rd this year. Next year I’m planning on doing an IM. I know a lot of people do a HIM about 8-10 weeks out from their full so I am wondering what the real benefit is. The difference in distances are so different that it’s not like one can work on pacing.
For pacing purposes it makes no sense. As you noted, you’ll learn next to nothing pacing a 70.3 at your 140.6 speed. You’ll learn more about pacing and nutrition doing a race rehearsal like 100 mile ride at IM pace + 1 hour run, then you would at 56 + 13.1 at the same pacing.
Just look at it as a hard training day and the benefits that entails.