Question re: LibreELEC-RPi2.arm-9.2.3.img on RPi3B+ vs LibreELEC-RPi4.arm-9.2.3.img on RPi4B

Running a couple of different versions of LibreELEC (as noted in subject, a couple of instances of LE on a couple of RPI3B+s and a couple of instances on RPi4Bs) I'm using Aeon Nox: Silvo skin on both and have loaded the Netflix Kodi addon (castagnalT/plugon.video.netflix) on both types of set-ups.

The Netflix addon works on both, but I'm finding that the RPi4B gets too hot running this (yes, I'm using heatsinks) whereas the RPi3B+ with the inferior RAM (1 GB vs the RPi4's 2 GB RAM) and processor stays a relatively cool 59 deg C - The RPi4B gets up to 78+ deg C (This has been tried on a couple of different boxes of both types with consistent results)

Why would this be? Is it a matter of something to do with the processing happening on the software side for RPi3B+ and on the hardware side for RPi4B ? Is there a way around this? Are we expecting an update that would alleviate this?

Quote from smp

Get a proper cooling for Pi4. Like a Flirc case or something like that.

Appreciated; however, it doesn't answer the question. The RPi4B runs perfectly well within the normal running temps for literally everything else. I pose the question though, not because I am unaware of how to improve the cooling of a SBC but because I wish to better understand the differences of the two OS versions with relation to the RPi boards. Thanks