Wow...that system performance lag must be hard to live with. I see this on my daughters laptop as well...ST4 seemed a little better in this respect.
Anyway, what you appear to have done in that video, is choose to edit the part in the context of the assembly, so trying to position the part there will have little or no effect. I suspect the performance lag may be partly responsible for the mis-selection of faces for alignment/mates.
If your placing a lot of the same or similar parts, try making a common feature set, [maybe a small cylinder] then use the "Capture Fit" command [look in help for more info] then placing the next instance will be a matter of selecting the target faces, in the corresponding order of mates set. A real time saver!
Design Manager Streetscape Limited
Solid Edge ST10 [MP2] Classic [x2 seats]