Well if it's up that high it just becomes omni-directional and its directivity on LW/MW won't be as effective. It should still outperform your wire antenna however. It's possible you have a noise source that is being amplified by the loop and thus creating a bad SNR.
If you had a SDR then you could probably detect this...
Ever thought about getting one? They're affordable these days...
https://www.hamradio.com/detail.cfm?pid=H0-015446
More info:
https://www.sdrplay.com/rsp2/
Video:
https://www.youtube.com/watch?v=92Ijh_NAEfc
devicelab-although the original subject of my thread here wasn't a S/N problem or loop performance, but was all about whether or not the sharp bend that I had in my wire antenna would create a pattern degradation or not, I can see where you're going with this. I do recognize the fact that you have a strong sense about an underlying problem I have here with S/N, especially on the loop. So, I will list all the villains my two antenna systems are up against at this QTH.
1. I live in a 10-unit building; all of which have computers, at least one of which has a plasma TV and that TV is right below me, and one of which has an ancient huge dish network from the 90s that gets him his Russian feeds.
2. There's a plumbing supply store right next door.
3. There's a glass shop next to him.
4. There's a neon sign shop next to him.
5. There's a school/ daycare/ church across the street.
6. There are power poles running along the south side and west side of my building; the south side ones are less than 20' from my living room windows as I am level with the lower utility lines and my antennas are level with the high power lines at the top that supply mega voltage downstream.
7. There is a 10-line TV cable bundle up on my roof that runs from one end of the roof to my end, right over my living room and kitchen and snakes down to the cable junction box just below my bedroom windows. The feedline for my 100' wire passes right underneath that bundle to reach the wire's feedpoint.
8. The feedlines for my Wellbrook and my D130j pass straight through holes that I drilled in the aluminum window frame of my bedroom to get outside; that frame is bonded to ground via the mesh and I-beam construct of this building.
With all of this, I am amazed that I get the mostly clean and reliable desired signals that I actually do get on all these antennas. Given all this, the mere fact that I could pull in a LW DX the other day over 2600 miles away, says a lot about steps I have thus far taken in making these antennas operate as good as they do.
Beyond all this, I am strongly leaning toward prcguy's balun suggestion...possibly for the wire AND the loop to attempt to squish RFI even more.