As gemmakermz said, just use a vee dop for stones with keel culets. You can use a cone dop for pretty much anything with a point culet.
Especially if you use wax for dopping, or if you use hybrid dopping with a wax “seat” and the stone glued in with CA (aka Crazy Glue). I don’t want to sidetrack the OP and start Ye Ole Dopping Debate, it’s just one of the advantages of using wax 😉
–Eric