There is no such thing as “combine”, the only thing you are doing is keeping the SSID of the Wi-Fi radio the same.
While, this is a highly debatable topic throughout, with no accurate answers.
I'd suggest, if you have not been having any issues with connectivity, then just keep things as it is.
Keeping the Wi-Fi name the same, usually allows the client device to balance between both bands as it sees fit based on range, load, b/w utilization. (Although in such instances, your AP also needs to be smart so that it can dissociate and steer as required).