At work, PR41AX, my colleague has a Samsung A70 running Pie. I too own the same phone, same model, same year, same O/S (Pie - same build and patch), identical phones. However, he is on EE and gets 2 bar signal 4G - not great but useable. I get ZERO bars, 3G speed (slooooow) and woefully unusable. We swapped SIMS and the result was the same, this time my phone was better with his EE SIM in.
Now if Virgin use EE network, and purportedly no loss in signal service, then why, when these two phones are bumper to bumper, is he getting a better signal than me.
Virgin do indeed use the EE network, but they don't have access to all the services & (in this case) 4G coverage that EE users do. Specifically...
EE have 4G calling (technically known as VoLTE) which enables voice calls over 4G, Virgin (in common with every other EE reseller except BT) drop down to 2G or 3G for voice calls. 4G calling enables access to additional 4G coverage on 800Mhz which seems to be available in this location. So the EE phone will be connecting to 4G800, your Virgin phone is connecting to a slightly weaker signal that's on a "standard" frequency.