Vetryan15, if you are 5 strand flat braiding you will have at least 2 strings per strand after you form the finger loop. When you get to the length of retention cord that you want and you have not spliced in any more strings, you will end up with a skinny split.
I braid left to right meaning I start on the left side, braid over 2 strings, then take the far right string and pass it over the 2 strings to the left.
To start the split, I take the top bundle (2 strings) on the left and pass them over the next two bundles. Then I take half a bundle (1 cord) and pass it over to the left.
There are now five strings on each side, so you braid one side of the split and then the other.
To bring the spltis back together, end the left side with three strands facing left and two to the right. The right side two to the left and three to the right. Run the left side two facing right over and under the two facing left on the right side.
Now bring the top left string down over three, under one and over one. Tighten the braid and bring the top right bundle (2 strings) down and over two bundles. Continue braiding one over two.
This is how I do it. Lots of other ways.
Pic on left is front view; pic on right is back view (the side ammo rests on) In this pic it does not look like the splits are side by side at the release end, but they are