Insulate cold roof with clamp felt, price

Hello forum!

If anyone can share their opinion or expert advice on this, I would be grateful :)

"What would technically speak against installing the insulation flush on the inside now and sealing it with the vapor barrier, so that the cavity remains on the ventilated outside? Nonsense or possible alternative solution?"

Attention opinion: I thought that was how it was.

Attention opinion:
I thought that's how it is.

"would be appropriate" would probably be the case if the thickness of the insulation matched the rafter depth :)
Since this is currently not the case for me, the question remains about the technically "proper" solution despite the missing 6 cm insulation layer.

In other words, whether the 6 cm cavity on the outside would be okay or should be completely avoided.
Hmm, seems no one really has experience or thinks that’s nonsense :)

Is buying another 6cm and clamping it behind an option?

I would not dare to leave a cavity between the underlay and the insulation. Possibly only if there are openings at the eaves and the ridge and everything is ventilated [behind] (this was how it was built in the 90s).

Is buying an additional 6cm and clamping it behind an option?

Actually, I've already considered that. If things turned out really badly, I'd probably do it. Before buying the 180mm insulation, I heard several opinions around me (including here ;)) that it wouldn't be a problem to use thinner insulation. After the purchase, I’m now hearing from several sides that it wasn’t such a good idea :)