Good XR and Poor XS signal strength

The image shows an iPhone XS (on the left) and an XR on the right. Notice the signal strength meter on the XS has only 1 bar and the XR has 4 bars. These are both on the same Sprint network placed right next to each other. This appears to highlight the problem I am describing--poor XS cell phone signal reception/transmission.

I visited our local Sprint store. They suggested doing a ##Update#. I did that. No change.

I visited our local Apple store and the genius bar. They completely reset my iPhone XS to see if there was a software issue. No change.

At the Apple store (Carlsbad, CA) they noted I made 44 calls and 2 of them were dropped. However, they did not show any indication about the poor send quality. Although both the send and receive audio drops out during calls. The send quality seems to be much worse. People frequently say they did not catch what I was saying. I have to repeat myself on a call. Over the past month I had only one call that lasted 1.5 hours that was flawless. Most of the others had problems with sound breaking up.

At the Apple store they checked out the audio in and out of the iPhone XS as well. There was no problem detected. The XS has worked flawlessly on music, Netflix and Youtube material. In addition I have tried AirPods, Wired pods and just the iPhone XS itself to see if the audio improved. No change.

Then I found the URL https://www.wiwavelength.com/2018/09/antennagate-2018-youre-getting-my.html

That shows the signal strength to be "low" for both the XS and XS Max. To me this is a strong indicator what I am finding is indeed a problem.

My wifes XR has worked just fine and my XS has been problematic. If this is a fundamental XS design problem, I may want to ask for an XR to replace my XS.

Any suggestions?