Plossl soft at edge in f/6 ?

I got my 10" Discovery mirror f/6 newt collimated pretty much on. ( By using a 2" catseye autocollimator, which proved much more useful, with the chesire, than the laser. The laser is only as accurate as the collimation on it, and that's a pretty coarse affair, IMO)
So in a moment between welcome precipitaion I went out and tried my tv 20mm plossl and a RKE 15, which are new to me, and both of them are soft on the edge, compared to my 12mm ortho.
I know this is an apples to oranges comparison, but do other people notice softness at the edge of plossls at f6 in daytime?
Thanks
Dan

I've never seen a Plossl (including TV offerings) that was sharp at the edge at F/6. Even on an Orion 80ED at F/7.5 the edges aren't completely sharp. The one time I've actually seen a Plossl sharp to the edge was on an F/15 7" Mak-Cassegrain at the local astronomy store.

Plossls are very good for the money, but they aren't the best for edge correction. On-axis, they are very good, and even up to about 75% of the field at F/6 they are pretty sharp.

Daytime testing shows many things that would not be noticed at night. I use daytime to test EPs many times so that I can see more aberrations. That said, the same EP might look quite good at night.
Take the 31mm Nagler for instance, a wonderful night time EP, during the day the look is not good, with a large orange circle around the edges. But at night, this is not seen and it looks quite sharp.
So, try them at night before you decide they are not up to par, unless you intend to use them during the day.