Tempo training is done quite often in many training plans often irrelevant of coaching philosophy.
I have always been a big believer in using Lactate Balance Point heart rate from testing to define the top of this Tempo range...and like to keep it tight with only about 5 beats below.
Since getting my metabolic cart and able to do some further testing by using a few different metrics from the results, I have been able to confirm this heart rate is still likely the best place to do this type of work on the bike.
The real difference is the athlete to athlete seems to be where this falls relative to the wattage they push at this level (as compared to normal testing) as well the heart rate as compared to their max heart rate.
Most programs would call for Tempo to be done 80/85% of max heart rate.
I feel now that the bottom of the range may be a little high for a number of people. I am finding that 77 to 80% is actually where many people should be doing Tempo in order to have consistent heart rate, power, lactate.
It is quite possible to get this number up to 85% of max but I believe that needs to be done by doing Tempo at the correct level in the first place and allowing the body to adapt to that stress level.
The picture shown below is of an athlete doing a 2x30 minute Tempo workout.
We have tried doing this 5 to 10 watts higher and just can't manage to keep all of the systems working together - wattage - heart rate - respiratory - RPE. When switching this session to data from the latest testing the 2x30 went extremely well and wattage only 5w off prior sessions at the end of it all.
So maybe try doing your Tempo at a point where you don't lose performance during the intervals by more than 3% and see what heart rate and performance that really is...you may also find it leaves a little more in the tank for other sessions planned during the week.