iPhone12 have lower communication signal less than iPhone 10, is it right?

Hello.

I recently changed from iPhone 10 to iPhone 12, but there was a problem with lower communication signal when I entered an apartment or building. Because of this, the phone was disconnected and there was an celluar issue, so I try to checked that there was no problem using the existing iPhone 10. This was determined to be a faulty device, so we checked the cellular issue of the device through Apple service center, telecommunication company, and Apple technical support, and recently, I wanted to receive a replacement within the device diagnosis and warranty period at U-Base ASP. However, the U-Base ASP confirmed that there was a yellow warning message on the cellular function after Apple Self Diagnosis, but found it clear in the action report. The iPhone 12 is supposed to have a lower communication signal. Due to the deterioration of ASP's performance when replacing smartphones within the limited warranty period, the U-Base ASP said to get Apple's technical support in a few weeks, and I still feel uncomfortable because of restrictions on phone and Internet use. While Apple's performance management and gains and losses on that ASP are critical, ASP believes it needs to strengthen Apple's brand identity and be more customer friendly. Please improve this and I will search for another ASP, not a U-base, and look for an iPhone 12 replacement within the warranty period. But is it true that iPhone 12 has less communication than iPhone 10? I'm really curious about this.