I don't really like to use the mk21's indoors for the most part. I feel like they end up picking up too much unwanted reverb from the room. If I do run them up close inside, I've found NOS works fine. On stage is a different story and ORTF wide has served me well.
Outdoor, open air recordings are where the 21's truly shine. I don't really hear much difference when using ORTF wide vs. NOS outside. I tend to run the ORTF wide if I'm really close and the NOS bar when a little bit further away. You really can't go wrong using the NOS bar with the 21's though.
I wouldn't expect you to, I've found spacing creates more of a difference then angle once I hit about 20cm and it's only 3cm difference between NOS and what we call a "wide ortf" (which is 27cm/110*). Anything past that and I'm getting more stereoness (for lack of a better term) with the time difference then I am with angle. I want the same approximate SRI/etc values so I use the 27cm/110* config outdoors more often as a result, but have used NOS before. The benefit of NOS comes in that you get a better on-axis response with the stacks or whatevers going on onstage. I personally favor the wide angle to help with level-difference stereo and not just time-difference stereo, but it's a personal preference and how the caps response off axis. There is the stereophonic zoom chart that will help with determining that (take an indoor config with cards that you like, find it's value, then look at the subcard charts and find the new spacing/angle combinations for that value). It's floating around on this site somewhere, but Redding has a
copy online too (look for the
hypocardioid for the relevant entry).
On stage is a different question though, the recording angle is much wider so I can pull off a respectable (but not overdone) stereo image with as little as DIN (20cm/90*) or if it's a really wide angle (almost on either side of each cap sort of wide) then I've even dropped it down to 17cm/100* and gotten great results with subcards. I hover around that 19-22cm area and shy away from going over 23cm though, that starts to push and pull stuff too much IMHO and it sounds sort of unnatural. ymmv.