Working with UHD clip in 1080 project

So I’ve looked at a few topics here in the forum about working with 4K clips in 1080 projects. Is it true the project size has to match the clip? The reason I would want to use 4K is to have a little room to push in and such on the final so I’m guessing the best workflow would be to comp the 4K clip in 1080 keeping the clips size and such then going into that comp creating all effects tracks and working that way. I tried tracking the 4K clip in a 1080 comp and got odd results. So I’m assuming the latter is the proper workflow. Oh and I’m using corner pin type tracks for ipad screens.

Thanks.

Yes, your best bet is going to be working inside a precomp.