G’day Jmayot, I’d advise you to accurately space the frames out. Leave 3mm from each side & 3mm between each frame. That’s provided your using drawn frames or foundation. If you accurately space the frames, as I do, the bees will place propolis around the frame lugs. That makes it easy when replacing frames.
If you want the bees to build natural comb, you’ll need to jam the frames up tight against the nuc frames. You can leave 3mm between the nuc frames.
It’s kind of asking for trouble if you place the frames in randomly. If a gap is too big, the bees will build an extra comb in that gap which is less than ideal.
I’m very meticulous with my frame spacing, therefore I never encounter any trouble in that area.
PS. We’re all still learning:)