MIMO antenna for T-Mobile 5G home internet gateway?

My Arcadyan KVD21 Gateway automatically switches, using B2, between N41 and N71.

For the first few days I recorded between 200 and 300 download and 20 to 35 upload.  Then it slowed down to between averageing 40 to 70 download 10 to 20 upload. Yet, this slower speed was more consistent.  When I was getting the higher speeds it was between 11:30pm to about 10 or 11 am the next morning until it started slowing and sometimes freezing a a few seconds or videos buffering.   It no longer gets over 175 download even using N41.  I think it's the trees growing here this spring.

I found out that the slower yet consistent speeds came from being on the N71.  The faster speeds came from the N41.  So, I've learned to trust the gateway to use the band that provides the best consistency.  Wondering what an antenna could do in this situation, I took the gateway and sat on the roof ridge for a few speed test.  The three tests were all just over 300 download and between 40 and 60 upload. 

If I want to optimize  the use of that signal that's on my roof ridge would using an antenna at that spot bring that signal providing over 300 download speeds down to the gateway where I place it in my house?  Or, should I expect it to slow down a bit?  (Based on the above antennas people have mentioned.)    ¡Gracias!