Just back onto the ergo after a very pleasant time of not being on it

Searched for a "get back into it training "programme.
Found Indoor Sports Services.
Worked out target pace for each zone based on very poor 2 k time.
Worked out HR zones based on 48 rest and 161 max.
First session last night was a AN session.
10 x 1 min on and 1 min off at 1.46 pace,HR 156 to 161
Came under the 1.46 but the session was not easy.
Next is my confusion.
My average HR was around 134, only getting up to 142 on the last two reps.
So far away from the expected 156 -161.
Hence my confusion, why is the HR so far away, were the reps too short?
On the bike I can get into 145 plus for 20 mins plus?
Thanks
Steve