Okay the way I have it configured for my use is to take frames in the original size. It can also be configured to resize them to any given size although you must give both x and y it won't calculate a change in the ratio its self. You tell it to take X number of thumbs (I said go ahead and take 5) and it then divides the video by that number and takes a frame at each of the calculated durations. Your video was 20 seconds, so they're about 4 seconds apart. I ran it once at original size and then again a 320x180 and gave you both sets of 5 grabs.
It's just configured this way for my use, but I can easily customize basically in any way you like. To take thumbs at a given duration, to exclude time from the begining and end of the clip from being included in thumbnailing.
http://www.serpentstudios.com/madalton.zip