This rifle would be for close in shooting and out to about 100 yards. Regardless of what I choose, it will have iron flip up sights anyway.
Everyone's eyes are different, but for </=100 yards I wouldn't worry about it. Let it flare into a big
blog blob, and fire away
I have the astigmatism too, and see a "comet" shaped blob instead of a red "dot". That said, I don't find it to be a problem unless I am shooting at 300+ yards.
Are you certain that the RDS is the problem?