You need to do this in two steps. If you want to have for instance 2 smalls units, and then 2 bigs, you start by making a munit in reduced size for the first 2, and then you create a second munit combining the reduced figure and the normal size ones. Warning: be careful with the size of the frames! Suggestion: if you want to reduce by 25% an animation, try when exporting in FLICSTER to select a size that will match the other after reduction. ex: The unit is normally 120x120. You want a 25% reduction. So with Flicster you export the animation twice, once with 160x160 size, one with 120x120. Then you use SBB to reduce the first one by 25%, so you will get a 120x120 animation, that you can easily combine with the other.