I suppose with smooth water snd s bigger wing andlighter weight you could maybe make it work.
I did it on my 800 wing, at 170 lbs, I have a 4m ghost and it would have been fine. And I was nicely powered on the 5m ufo.
The nice thing was it got me warmed up but was a lot of work, the kite is fast and has a decent dive so it can get you up but you only have. 3m of stuff to pull you if you don’t move it, you will not be getting enough pull.
I agree with Grigorb, the ghost is a more normal feeling kite. The 4m ghost is 50 grams heavier than the 5m ufo so still pretty light and a lot of fun but it is not the same as the ufo.
So could you make a 5m and 3m ufo work? Sure but beyond the difference in power there is a big difference in speed.
So example coming from the 4m ghost to 3m ufo not so much of a big deal, coming from the 5m ufo to the 3m ufo, well that requires some adjustment.
That is one thing I think board riding Maui really got right (besides a bag with no zippers) with their cloud, is constant percentage change in kite sizesl
2m gaps between all of the kites doesn’t make much sense to me.
So write to slingshot and tell them to make a 4m ufo.