I like @anon67840561’s strategy. Back off a little bit in that first lap until you hit some steady state pain level, then try and hold that through the first half of the race. In the second half, if you are feeling better, you can up the intensity, otherwise, hang on for dear life.
My max HR is typically low 170s and during cross races my HR varies between 156 and 165. I don’t look at my HRM during the race, but I am constantly checking the what level of pressure against the pedals my leg muscles feel. If I notice that the pressure is lighter than it was the last time I checked, I put more effort into pedaling. I don’t really check when the perceived pressure is high, because usually that means I am chasing/being chased by someone and just need to keep doing whatever I am doing.