Many radios have more margin on the signal once "connected". I vaguely recall that cell modems in particular need to do an initial registration with the network

Many radios have more margin on the signal once "connected". I vaguely recall that cell modems in particular need to do an initial registration with the network. That registration is probably at a fairly ancient modulation, without the benefit of the cell tower knowing where the modem is to beam form to it. It seems like that could account for 10's of dB of difference.