I would split them up, it won't look right if you have one type running the length of one bed and another type doing the same.
I would suggest that you mix them in and tie them together for a more unified look or your yard will look choppy.
I would also second the suggestion of adding in some other plants.
The two that you have picked are both a shade of purple (unless you got the white liatris) and you say you have russian sage which is also purple, so I would add some other plants of at least one other color, I like orange with my purple flowers, I planted orange yarrow with all of my anise, lavendar, russian sage, liatris etc.
I like the gracefulness of the agastache anise and it would go well with the colors you have and will soften the lines you have now.The bees also LOVE it!
The russian sage is the same way, tall and graceful but the agastache is a little more thicker, fuller plant.
You also probably should find some plants that are lower growing and more of a round, mounding type.
Those will give it some weight and anchor the space.
If you want to fill up some space, sedums grow quickly and get big and roundish and change right up until fall.
One thing I like to do is to carry at least one type of flower throughout the whole yard, I planted agastache in all of the gardens I have to bring a uniform look, even though all of the gardens kind of have their own thing going on.
You have picked some nice flowers, I have all the ones you have mentioned, it seems the majority of plants I love turn out to also be purple.
Thats why I throw in a burst of orange (yarrow) or yellow (rudbeckias-black eyed susans) here and there.
I use others as well but can't think of them right now.
Just be careful of not using enough of anything to make a statement, get several of each plant you are going to use or else the gardens will look disorganized and lost.
Good luck with it and have fun!!