Actually, you don't want to arch when doing only one layout. The tight arch used in the double layout is to make your body flip fast enough to rotate twice. If you look closely, the arch doesn't really show itself until she enters the second layout. I think most judges will take a slight deduction if you arch a single layout flyaway.
I've never seen your tucked flyaway, so I don't know how high it is, but you may need more height for the layout. Be sure to get a good tap. When you release, squeeze. The girls that I have taught to layout flyaway ended up liking it better because with a nice tap, there's less to do. If you tap your toes high enough, you can pretty much let go and float to your feet. You don't have to do much to cause the flip. You can't' do it that way forever if you want to add the extra flip and twist, but it's a nice way to get used to doing it.
My legs would immediately tuck as soon as I let go of the bar! 
Any suggestions?
keep up the hard work
