Actually, the hard koshita never bothered me or caused me any problem. I can't say I feel it very much or hurt during practice, no matter how much or hard I take ukemi...
And when I say the koshita are tied in the back, I must pointed out that I let them hang inside the hakama, not outside. The koshita from the "back panel" are tied in the front. So, unless you take a very careful look at how it is tied , you will never noticed that the koshita from the front panel are tied in the back and hanging inside the hakama. You will just see what looks like a normal koshita knot.
A few years ago, I was able to tie them in front. Now, there's just not enough length. This strange phenomena also happens with my everyday pants. Now, I'm not able to tie pants that were just fine a few years ago. I suppose that clothes just get smaller at the waist with time!