Hooking up 2 BEC without going thru RX

[_paralyzed_]

Nope, still wrong, you are tapping off of one battery, you need to power the bec(s) off of BOTH BATTERIES.

In your second diagram you have the bec's positive power source hooked up to the positive of pack 2, leaving out pack one and only giving you half voltage.

Leave the negatives where they are on your second diagram, but move the positive power source for the bec(s) to the positive wire on pack one (not pack 2 like you have it.

To clarify- you want the full 6s powering your bec(s), and you are trying to tap off one battery. You should use the same positive and negative battery cable you plug into the esc to power the bec(s)

Your new way solved the floating ground issue, but you always want to power off of both packs, otherwise one pack will be depleted before the other, and that's no good in a series set up.