Thanks for tagging my in on this. Sorry it took me two days to get here - LOL
@onion - it's small size of the single 1/4in RFG would certainly cause restriction in this case. Simply due its smaller size and the higher flow that pump can produce
The Axis pump I believe has a max flow rate of around 400 GPH, and assuming that the photo you posted is a with the pump at 100%, I would say we may have different issue. With that pump at 100% and the RFG in that position you should be seeing a wide flower-like spay [pattern coming out the RFG. Not a trickle like in your photo.
I would inspect the RFG and the other parts the flow kit, for some sort of obstruction. It could be a small piece of rock or even a stominela snail shell
With that said, If you goal is to use the the Random Flow Generator as your only flow the tank, then going to the single 1/2in is a good option. It will do a better hob of converting the flow form that pump (300-400 GPH) to a more usable flow that fills the tank with movement
Before you do that though, lets figure out why this seems so restricted. Are you able to post a short video of the pump at 100% and at a similar angle to what your photos above is?