Is RHR calculated different compared to Forerunner 935?

Hi There,
So I've had the Epix 2 for about 10 days now, I upgraded from the Forerunner 935. 

I understand the Epix 2 has a new HR sensor so it should be more accurate but I am finding the RHR readings I am getting are a lot lower compared to my 935 so I wondering if there have been any changes to how the RHR is calculated between the newer units over the old? For the sake of example, on my Forerunner 935 I would have a 7 day RHR average of around 52 bpm, and on the occasion I might record a 49 one morning, but largely it is consistent around the 52 over the course of the year.

As soon as I got the Epix, I started recording 47,48s, last night a 44 and the highest RHR I've recorded so far is 51 after a late night. 

I don't think the watch is broken as my workouts seem about right.
Has something changed?