gypsi, i have found moving nucs to a different location to be of great benefit until they build up enough to take care of themselves. i have the luxury of a few different places to take them, but usually start out with the smallest entrance (like mm said) on the nuc to guard against any robbery of neighboring bees. so far, haven't had a problem with neighboring bees when moved.
a nuc left in my yard for the past 5 or 6 years is sure to get robbed out, so when i make up nucs, they are moved. like you said, 20 ft is not far enough, 2 to 3 miles would be good, or like what you are doing by moving 25 miles, but also be aware again of any neighboring bees. good luck to you gypsi, and i hope moving them works for you so they can build up for you. post an update here after you moved them to let us know how they are doing.