Here is my general advice for cross chokes in the absence of any other answers. I don't personally play closed guard, but I think most of this advice should still be applicable.
The goals for a blood choke are roughly, in descending importance:
- Target carotid arteries
- close space
- maintain pressure
- maximize pressure
For cross (your arms are crossed) collar chokes, I want my hands as far around the back as possible, to the point where fingers from my two hands are touching. This puts the pressure from the forearms on the carotid arteries.
In judo, there are three recognized variations:
- nami juji jime (both palms down)
- kata juji jime (top hand palm down, bottom hand palm up)
- gyaku juji jime (both palms up)
What's missing is the combination where the bottom hand is palm down, and the top hand is palm up. For the top hand palm down variations, you can lift the chin to expose the arteries and get pressure off the jawbone.
To maximize pressure, you want the smallest surface area in contact with the arteries, so use the side of your forearm or wrist and not the flat surfaces.
In my opinion, once you cinch the choke, it's more important to simply maintain the cinch than to apply more pressure. In this view, scissoring the arms is about cinching, rather than about applying overwhelming force. You need to make sure the opponent does not have the space and opportunity to break the cinch, either by inserting arms between you, moving their body, or pressing your elbows in. Pulling them in is one way to make it harder for them to move. Another way is take away their base and cause their weight to be partly supported by the choke.
Personally, I think the both palms down version is simplest to understand the principles of a cross choke, but is the least realistic to actually get in live situations.
It's also frequently beneficial to sweep and finish the choke from top position. The choke draws attention and makes sweeping easier.