For testing I am just using the quarter wave vertical, without any form of groundplane for now.
The actual project will have dipoles at least, but at the moment, I am just comparing apples with apples.
The same quarter wave wires on the SIM20 modules ( in fact I noticed after the test that one was only 120mm long instead of 170mm ) at the same power give me 500m range, but as I said I dont trust my setup, and cant use the spreadsheet on my PC.
I will have another look at these modules one day when I have time, but this is a rush job now.
( I worked with diversity combiners in the 60s, and wondered what happened to them since, the first time I noticed them on commercial equipment was on base stations for wireless mics 40 years later )