Place RadTransitionControl with size 200x100 inside of ViewBox with size 400x250. Available in LIB version 2015.2.803 , it will be also available in the 2015 Q3.
I get a similar issue when using the transition control under high dpi, the copy of the current screen gets shown at about 75% before fading out. I'm guessing there is some adjustment that needs to be done when running in anything other than standard dpi.