I'm not really sure what you're describing here.
Did you batch prime? With 3/4 of what amount of corn sugar? When batch priming, I like to use one of the online calculators and weigh my priming sugar to accurately get the level I'm looking for to fit the style and my tastes.
If you're placing already primed beer into the 5L vessel and have the correct amount of headspace, I would think that it would carbonate just like in your bottles.