I just thought I would add my 2c here in regards to the flat clear coat to give an idea of how they work. Once you have a solid understanding of the product, spraying it is much easier to get consistent results.
Matt/ satin clears are regular clears that contain silica. For anyone unsure silica is a glass. The glass particles are degraded in acid which gives them a very rough texture. Silica is what we call a migratory pigment, as the solvent evaporates from your clear and dries, the silica all floats or migrates to the top of the clear coat and distorts the light refraction. The higher the concentration of silica, the more matt the finish will be.
The secret to spraying matt well is 2 things, drying time and wetness of application. The longer the product stays open (wet for) the longer the silica has to all find its way to the surface, so if you can retard the product it helps. Its an advantage to apply the coats as consistently as possible and reasonably wet. A second coat once the first has tacked off will actually pick up the silica on the top of the first coat and carry it to the top of the next coat! Again the clear needs to stay open for as long as possible to achieve a consistant result.
Snapdragonxxx now the issue you showed with the frosted area is where there is a higher concentration of silica and your getting more light distortion. I would almost guarantee a second, wet coat of matt clear would have evened the finish out. It may not be the way you choose to finish your work but I thought it may help explain the process taking place if you wish to ever trial it again. Also of note the bigger the fluid tip of your airbrush the better, and while high pressure gives you nice fine atomisation when putting colours down for a nice thin coat, too finer atomisation of your flat clear will result in a thin coat that will dry too fast.
One other thing to note, that concentration of silica on the surface of flat clears will slightly lighten your colour, the more coats the lighter it will become. Oddly enough you get the opposing effect with gloss clears with the more coats the more you darken a colour.
Edit to add not all matt clears are created equal and give different levels of matt so testing panels is always an advantage. Most of the modelling specific clears should be ok but for people using various aerosols perhaps intended for art and craft etc it would be advisable to test.
I hope giving the information is ok and might help a few people.
Josh