for anyone who may be interested...
it's not as if this was some great problem or bug that needed a solution, and the main reason it took me a while to get it right was because c2 simply doesn't have all the conditions that would have made it simple...yet. like "if", "else" or "or".
but, as a noob with any engine, i usually start with implementing space invader movement to gauge how easy the software is to learn, and how simply it can create this straight forward movement type. and without being complete, it got the job done.
i ended up having to separate the enemy movements from the side barrier collisions, to get around the picking thing. and i had to check for 'down' first, separately from the left/right checks. i also had two variables tracking movement; enemy_direction was a text variable that tracked down/left/right, while enemy_interval tracked just the left/right interval.
so there you have it. a whole lot of hulabaloo over something not that important. but i hope it might be of some help to other noobs.