Heart Rate: TT vs Road Bike

For those who train on both TT and road bike, just wondering… how does your HR compare on them at the same power?

(This is assuming in full TT position on aerobars vs riding in hoods on road bike)

I just did the first session on the TT bike in over a year, and was surprised my HR stayed so low. On the one hand I am leaning on the arm rests, but on the other I am in a pretty low position with restricted breathing. Here’s the data from today’s session with a Z2 road bike session in blue: