Heart rate question for short course folks with power

As a non power (no PM) rider when I get into the bike I ride easier than I think I should on a RPE basis to settle in. It seems to take a while (20mins) for my heart rate to drop into the range of %LTHR I should ride, but before that it always bottoms out lower than that (90%). I end up pushing a touch after to bring it back up, so that brings up my question. As a %LTHR, where do guys that aim for a level VI land when they’ve settled in? Do I need to press just a touch more from the start or keep letting everything settle but press a bit sooner? 64 minute oly bike so I’m not FOP but starting to look for places to squeeze out those seconds.

You’d probably be better off riding by PRE vs HR.

I am riding off RPE, my question is “based on another variable is it possible I’m leaving time on the table?” That’s why I’m curious about where %LTHR lands for people that ride steady power. I know it’s an “it depends” situation but I’m curious about consensus.

Yes it’s possible. 2-5 minutes to get the legs going and off to the races. 20 minutes is to long to get going in SC racing

I use a PM, but 90% of FTP works out to about 95% of LTHR for me. I target 90% for Oly.
LTHR is 163 and 153/154 is about where I get to 90% of FTP. RHR is probably 48 to 50.

I don’t have much trouble getting to 153 quickly. Swimming gets it high from the get go.
I don’t pace by HR but I do use it to cross check.