Satin or semi-gloss wiping varnish settles VERY quickly. I suggest you brush 2 coats without thinning. If you are using a wiping varnish; I don't use "Arm n Seal" so I'm not sure if it's a wiping varnish or a regular poly. If it's a wiping varnish you will not get much better build than wiping varnish without the flattening agent settling in grain which may be causing your streaks.
Applying a wiping varnish with a brush is NOT the same a brushing a regular varnish coat then sanding it back. The wiping varnish is much thinner and will not act the same.
Scott
Finishing is an 'Art & a Science'. Actually, it is a process. You must understand the properties and tendencies of the finish you are using. You must know the proper steps and techniques, then you must execute them properly.