It is correct that for different FOV's you can only match the sensitivity perfectly to one specific method. The difference between 103 in PUBG and 106.26 (if you have a 16:9 monitor) is very small though.
You need to set fov_cs_debug to 86.63 to match 103 in PUBG (with a 16:9 monitor), but as you probably know this only works on custom games with cheats enabled in CSGO.
Unless they have changed anything in PUBG lately you can alternatively set the FOV in the config file to 106.26 instead to match CSGO.