I do not know for certain, but I believe @Jose-Albacete uses about a 6 inches or so interstem to give him room and make compatibility work? Hopefully he’ll chime in. I know he’s posted about it at least once somewhere in this large thread:
https://growingfruit.org/t/ranking-of-varieties-of-cherries-only-high-quality-varieties/33702
Either way, yea, I recommend having at least a bud on the adara scion as backup. I find it takes quite easily on bark grafts so that way it should a near guarantee that you can keep the adara at least.