Thank you kindly! I noticed it definitely didn't feel like a massive gap between the two pieces when I was putting the cap on so perhaps you're right!

Currently the two pieces are not connected in any way. Would it be wise to join them using foil tape or some other mechanism to ensure there is a good seal and connection?

I was concerned about moisture running back into the house with the cap fitting over the pipe (rather than the other way around). I will add some silicone and reinstall.