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Here's a heart rate plot of two recent crit races I did. Note that the Heart Rate axis does not start at "0". Sunday "fall river crit" was a 3/4 field, Wednesday "witches cup" was a 4/5 field. A couple notes about each race:

Fall River Crit
-Sunday Aug 12, 12:15pm
-cat 3/4
-20 miles, 20 laps, 1 mile per lap
-one 60ft hill per lap @ 4% grade
-not too much braking required on the four-corner course
-i did the 4/5 race 8am that morning, rested in between, 6-mile warmup 30 minutes before race
-perceived effort was very high on the hills, but very low elsewhere

Witches Cup Crit
-Wednesday Aug15, 5pm
-cat 4/5
-45 minutes (18 miles), 36 laps, 0.5 miles per lap
-about as flat as it gets
-turns were a bit tighter, more accelerations required coming out
-two-day recovery prior to race, 20-minute warmup just before the start
-perceived effort was medium to high, less than fall river for sure

I'd like to try and figure out why my heart rate was so pegged throughout the Witches Cup Crit, and why it actually came down significantly at the Fall River Crit. My best guess is that it's because I had done another race previously that day, and that my muscles were more adequately warmed up. Would this explain for such a difference? Another theory is that the downhill portions of Fall River allowed for more rest, thus the decrease in heart rate, but I would describe Witches Cup of having similar slower periods where I would expect the heart rate to come down.

What's the point of warming up anyways? I would expect to see some sort of difference in my heart rate data as a result of properly warming up, maybe this is the kind of difference I should expect.

I can't see your HR data, but just going off of your description of the race I would think that having to do more repeated accelerations out of the corners is what kept your HR higher. Of course, your racing different fields on different days so there could be some other factors. From personal experience, the toughest crit course I've raced is one with short straights and alot of sharp corners..My HR stays consistently about 10 bpm higher on that course. That is in comparison to a course like Cat's hill in california that has a 23% grade hill in it that is about 100 yards long, but you able to recover and drop the HR on the back side of the hill. If you had power data you could compare where you were having to put out the most power on each course and where you were having to sustain it.