Vodafone UK SIms in Miami will under perform compared to local in country SIMs. Often when roaming like this your internet traffic will get routed via the home country for accounting purposes, and if it does then you’ll take a bandwidth hit due to increased latency.
Looking at your numbers above I’d be interested to see the physical install of the Poynting antennas. Cellular 3’s high SINR suggests that it is in an area with a higher level of background RF noise.
Cellular 1 with its antennas up high away from the rest of the vessel has much better SINR on those same frequencies (Band 2).
Look at the B12 on Cellular 2 sitting there with SINR @ 13dB and a RSRQ @ -13dB thats interesting.
And the cellular 4 - is that antenna inside or just a lower gain antenna element I expect. Either way, the reduced reception of signal is working well on that module as less noise is being received so the SINR looks better.
I think you’re in an area with a high density of user equipment (smart phones / routers etc) likely a marina. The antenna at the top of the mast is more distant from those devices working at sea level and so is getting a cleaner signal. Cell 4 is either having its signal attenuated by the vessel itself (which is blocking a chunk of the crap noisy signal), or it just has lower gain antennas connected so less noise is being picked up.
I’d be tempted to force the other cellular modules to use B12 too and see what happens.
Do check what your public IP is on the VF UK SIms and then geoip lookup to confirm where that IP breaks out.
Also speedtest across all cellular modules individually and let us no the results for comparison, I suspect that you’ll find you get the best results using the mast head antennas and the internal Mimo because of the level of RF noise in your vicinity.