spraying clear coat

Along the same lines as the windex, I use Tamiya acrylic thinner with my future to thin it out.  I get glossy coats without the sandpaper texture everytime now.  You could always try putting a little of the thinner you use with pollyscale in it and shooting it on spare plastic to see how it comes out...

If it doesn't work, the lower spraying pressure and/or spraying closer to the model are the best ideas I can think of.

If the clear coat is acrylic, then a arylic retarder will help. Also, lower the air pressure. I spray FUTURE at ~10 psi. Sometimes even lower.

I've found that (with Future) spraying pure windex over the model after about 5-10 minutes of drying really smooths out the finish. Not sure if the retarder or thinner for polyscale will have the same effect.

Temperature can also have an effect. Spraying at a very cold temp can effect viscosity.

Is that an acrylic? If it is, put a couple of drops of retarder in your colour cup and it should fix your problem .

Rich