depends what look your going for mate, I think its common to have it towards the rear especially in a tank size like yours because they do grow quite tall, but obviously no way near as Vivapara but the vivapara didnt seem to spread for me, its a very annoying plant to maintain but as I have said before if you trim the new growth at the tips it will help to keep it in check. My opinion on the planting would be to plant at the rear around the vivapara and when its fully carpeted and spread out just give it a gradual trim so its lower at the sides and higher toward the Vivapara. Just a thought. What ever you do I am sure it will suit.
All the best mate