It was mainly because I had been looking at uprated gmade shocks and could find some in the length that I needed for them front, but not the rears, so wondered if they could be put the same, but I hadn't thought of the shock tower being higher, I thought for some reason the back wheels would be extended lower, essentially putting the front in a nose down kind of fashion. But what you said makes a lot more sense.
I shall try adding some different shock fluid and see how it goes. Do I need any kind of sealant after taking them apart and putting them back together to keep the fluid retained?