LB1120 download speeds not as good as iPhoneXr

I just got an LB1120 and have an ATT sim in it that's on the ipad unlimited plan. The modem gets 4 or 5 bars, but the download speed seems to stay between 30-40mbps and can't sustain higher. Testing at the same time in the same room on an iphone xr on an unlimited prepaid plan I can easily get to 100mbps. The weird thing though is the upload speeds on the LB1120 are always between 20-25mbps which is impressive, while the iphone can only sustain 10-15mbps. Is the download speed a limitation of the modem? Is it possible the different data plans are giving different speeds? Thanks for your input.