Scaled clips on 4k timeline look worse when exported back to 1080

[soaringchicken]

Working in a 4k sequence with mostly 4k footage. A few 1080 clips are scaled to match. When exported to 4k everything looks fine. When re-exporting for social media at 1080 the resulting export shows all the clips that were digitally scaled to match the 4k timeline looking even more pixelated than they did in the program monitor.  If I take that 4k sequence and then nest it into a 1080 timeline and export to 1080 the resulting video shows the clips that were digitally scaled to match the 4k (and now all scaled down to 1080) looking as they should, no excessive pixelation.

This has got to be a really common issue for anyone working with scaled media (lots of people) and who wish to export at native as well as downsampled resolutions (also lots of people).

As much as I'd like to know what's going on...(some sort of sampling math problem?)...I'd love to know if there's a fix other than having to create a new sequence for every lower resolution export I'd like.

I've tried this with every export format and codec and checkbox and hardware vs software encoding.

SPECS:

Premiere Pro v 24.1.0

Windows 11 Pro

i7-8700K

gtx 1070

64gb ram

[Ann Bens]

1080 in a UDH timeline wont look all that good. You are scaling to image up by 100%!!

  If I take that 4k sequence and then nest it into a 1080 timeline and export to 1080 the resulting video shows the clips that were digitally scaled to match the 4k (and now all scaled down to 1080) looking as they should, no excessive pixelation.

By @soaringchicken

That is the way to go.

If you want good scaling go for Topaz AI.

[soaringchicken]

I understand that 1080 to 4k is a %100 scale and a doubling of pixel size if viewed in a 4k program monitor at 100%. But if that is then scaled down in export to 1080 then those pixels should shrink back down to their original size. Instead the result is worse than if I had not done any scaling.