usually some clear coats doent require reducer. i only use reducer if it is extremely hot to help flow out a little better. sometimes if you use too much activator the clear will want to run, i dont know what kind of system you are using but you might want to double check the mix ratios and make sure you are mixing it right. i hate runs because i can never get them completly sanded out unless i use a da and reshoot. also 2:1 sounds a bit too much activator, you can try and step it up to 3:1.
what i use to do when i had problems with runs is do a tack coat. this means spray the clear coat on dry, not wet, kinda like a light-medium coat. you want to spray it on as even as possible also. now this will look kind of crappy, itll look kinda dull but thats ok. now if its kinda cool you might want to wait a while until putting on the second coat. this is where people usually get runs because they dont wait long enough. in a non heated booth i would wait about 15 minutes, touch an area that will not be seen or touch paper and if it feels wet then wait a little bit longer. if it feels kinda sticky then its ready to go. apply second coat in a medium heavy application, make sure you get it even. also try not to double coat, stick to the 50/50 rule. wait a little bit longer then put the final coat on about same thickness as second coat.
the use of tack coats kind of helps the second coat to stay in place. hope this helps
