This mod essentially has the player guess what a modded radars range is, and it bites because that method results in inaccurate marker placement.

This other mod though: https://mods.factorio.com/mod/RadarGridGuideStrom seems to just say "press Ctrl G with mouse hovering over a placed custom radar" and you know what? it works. You just mouse over open air after that and hit "Ctrl G" until it shows a white box for placement, and it's accurate.

It spits out some info about what the range is on the custom radar then, but not in any format that's useful to this mod. Instead it seems to work in chunk numbers, instead of whatever unit of measurement this mod uses. could you look at this and copy pasta the ctrl g part? or find a way to let players figure out how to convert the info it spits out into your unit of measurement?

also the custom radar i was using: https://mods.factorio.com/mod/Roboport_and_Radar_MK2