I never had Cardinal Tetras only Neon Tetras, in the past and present, and both are said to have the same habits.
I presently just have a 10 g tank with 7 Neons.
They tend to school and hang out in the lower portion of the tank...... from about the middle of the tank to a bit lower .... and sometimes even bottom feed.. They are voracious eaters..
The tank is heavily planted and they will sleep scattered all over the tank among the plants..
BTW, I also have 3 Harlequin Rasboras (I'm looking for one more) and they school and feed a bit higher than the Tetras..
They usually sleep in plan view..
The two species get along great together and make ideal tank companions . :