once frame stack starts to change dramatically, this is when comparos become slightly more difficult. some bikes have a long headset cup which changes the lower stack you can use. Others have cut steerer tubes. others dont. this is why stem length/degree combos are useful to achieve the effective handlebar stack/reach position you want.
Your stack/reach comparo is a good start. but dont be too critical, because like i mentioned there are other factors which may change your preferred fit. different frame geometries can work similarly well for you when comparing from bike to bike.