All of the network selection/registration is done by the u-blox firmware. The Mayfly’s mcu tells the Digi mcu to tell the u-blox mcu to automatically select the network. ModularSensors doesn’t even both to ask which network gets selected. It could ask, but I never cared enough to implement it.
ModularSensors is also requesting automatic selection between LTE-M and NB IoT and the same telephone chain makes it happen. But, in reality, if you’re using a Hologram SIM, you will never use NB IoT. Hologram doesn’t currently support it in the USA. (https://community.hologram.io/t/nb-iot-usa/3434/7). All of their advertising makes it look like they do, but if it’s actually true for anywhere in the world, it’s not true for the USA.
I have the Tagolas Maximus that Beth linked, the same Pulse that you have, a PCB trace style antenna from a GPRS bee, and a unknown brand (came with a kit) stick antenna with an SMA/uFL adapter currently on my desk. Right this instant (literally right now) I’m seeing CSQ [scale of 0-30) of 12-16 with the Tagolas, 17-18 with the Pulse, 17 with the PCB antenna, and 18-19 with the stick antenna. (Yup, I just yanked the uFL off that many times just for you guys.) I personally prefer the little PCB trace antenna. I pretty sure the reason my big Tagolas antenna is so much more variable and lower than the others is that it’s big and thin and has gotten crumpled up sitting on my desk (hence my preference for the stiff PCB antenna). When using the flat patch style antennas, the orientation of the antenna and the cable can make a big difference – the data sheets for them have pictures of the exact amount of curve they’re supposed to have. Running any power cables the wrong way across the antenna can also kill you signal. (Remeber how one of the iPhones once had a warning about “don’t hold them this way” or you’ll get bad service?)