Personally, out of habit, if I plan a render in 4K I keep the resolution of the TL in 4K and as I have an external monitor in HD, I set the output scalling in HD.
In the delivery, you then choose the resolution of your render.
You can also do the opposite test: with a 4K clip, you choose a TL in HD, you put a Lens Flare with tracking (or other effect) and then you change the resolution of the TL in 4K: you must not have offset in the render.
This is the independent resolution (timeline resolution).
(do a search on the site: there are several trends: some do like me, others differently)
HD_DCI00086496.jpg
4K_DCI00086496.jpg