my tank is 18" wide too and I am currently using a Coralife on legs.

It is very flexible as you said since you can move it back and forth...which makes it even easier to work in your tank...and the beauty of the plastic legs allows u to have an open top tank...

I'm using only 2x96W and find it kinda hard for the light to reach all the way.

So having 2 seperate strips would really help.