How well does this work for you without overshooting your higher HR? I find with kettlebells, my HR spikes about 15 seconds after I put the bell down, so I have never felt like it could be a steady state modality. My HR is way too spiky with a kettlebell for that.
This assumes that the maximum HR is more meaningful than the "average maximum". Some people's HR are spikier than others. I don't know if that's meaningful or not (I suspect not).
And if the actual max is not meaningful, then round those spikes off and go by the "average maximum."
And really, some of the spikiness could be in the sensitivity of the sensor, the graphical representation of the raw data, etc....
All this to say.... take the HR graphs with a grain of salt and don't let them talk you out of something that you know is working for you.