I have done both many times.
Starting them at the top seems to work a lot better.
If I place the frames in the bottom, often times the bees will beard to the size of a smurf basket ball at the outside entrance. And then swarm, somethings super swarming (multiple swarms).
My preferred method now is to place the frames from the top, 2 full frames, then place the 3 remaining frames to the bottom and place 3 foundationless frames, with waxed wood strips in the top slot next, nest to the frames with the bees.
I have started the observation hive many times with just 2 frames of brood and the rest foundationless and they usually just beard outside and then swarm. When they start to beard, I now add a frame or 2 of drawn comb vertically and they go back inside and start building a full hive instead of swarming.
Jim