Different content has different bitrates. I think all 4k content was 15.62Mbps and is now 7.82 or something. Not sure why you are getting 4Mbps for Into The Night which is 4k content (unless you are on the HD plan, which I can't test).
1080p Content has a variety of bitrates (not sure why!) The Thing is showing 0.81Mbps for me, so was probably 1.62Mbps originally. Generally older films are lower bitrate, but there are exceptions as I just tried Event Horizon and that's showing 5.52Mbps so that used to be 11Mbps which is the top end for 1080p content.
rp2000