rootstock vs scion cold hardiness

[incubator01]

I bet this will probably be perceived as the most stupid question ever asked, but i kept banging my head over it anyway.
One of my kumquats is grafted on a volkamerian rootstock, which is said to have a low cold hardiness of about -2 °C, but the scion is a nagami kumquat and kumquats are sead to be cold hardy to about -7°C (give or take, i may be a degree or 2 off but anyway)

My question is, does the scion take the cold hardiness of the rootstock (in this case, would it die at -2°C) or do both parts have different temperature tolerances?
With poncirus trifoliate i already know the scion inherits some of the cold hardiness but I don't know how it works when it is the other way around.

and yes I was planning to overwinter it in a semi sheltered environment with frost cloth but it's just to know if I need to equally protect it or add a few layers extra around the rootstock.

[vnomonee]

I have a kumquat on a type of sour mandarin rootstock. The kumquat is hardier than the rootstock, but that it is how it came from the nursery I ordered from. It's in a pot so I'm only worried about root rot from the mandarin rootstock if I overwater it (which through research I found is an issue with this particular stock), not worried about the elements since I would move it inside during the cold winter.

My guess is if the rootstock succumbs the grafted kumquat part of the tree is going to suffer regardless not necessarily dying from the cold but if the bottom of the plant is no longer alive it would die off as well from lack of being able to uptake water, nutrients, and such. You could probably save the kumquat portion by grafting it to something else though.

I'm planning on grafting a bud when my trifoliate seedlings get bigger to have backups in case I have trouble with my rootstock on this kumquat.

[incubator01]

well since I was already planning on wrapping the entire tree in frostcloth layers despite it being in a semi sheltered place in the winter, I shouldn't be too worried, but since the scion part is so big (it's a 2m high tree) I thought of wrapping only one layer for the scion part and several layers for the rootstock and graft union, provided that the scion would be able to survive a few degrees celcius colder
Worst case I would only loose the top branches, since they're closest to the roof. The container is on an elevated platform with wheels so the ground temperature will prove no problem either.

[Citradia]

Your tree will be less cold hardy in a container weather you wrap it in frost cloth or not. In my experience, frost cloth does not help much if your freezing event is very long as in a 24 hour freeze or longer. Unless poncirus, potted trees should be put in a shelter/cold frame/ greenhouse if you live in a zone where it freezes more than a few hours a night a couple of times a year. Remember you will probably have to keep overwintering meiwa fruit from freezing on the tree too.