I don't think it actually matters that much if they aren't the same. Damping occurs via both tubes on the up and down stroke, so they are both acting all the time.

I'm also not that convinced that having two tubes is really necessary at all. The geometry doesn't change that much as the chassis rolls, so identical set-up of the tubes left to right shouldn't be that important. The shock cars don't do anything much different to tubes, and I seem to recall that one of CRC's early cars had a single tube running on the diagonal.