As much as I adore Arwen's work, from what you are saying, it doesn't sound like her tweaks are likely for you. (Just a feeling)
That having been said, I do understand what you're saying and looking for -- the fact that crouching vs. standing is an automatic failure to sneak - even if you haven't actually been detected yet - makes little sense to me... particularly since there are instances where it shouldn't make all that much of a difference (something that happened to me a while back: standing in a shadow, stealth boy enabled, trying to snipe an overlord in the head from long range - but couldn't get the right angle unless I stood up... I still wouldn't be detected by anyone, but lost the stealth crit by doing so).
...so while on the surface a mod to allow sneaking while standing sounds like "a cheat", I guess I could see something like a moderately high level perk with high requirements that allowed for some limited amount of continuing to sneak while fully upright, difficult as that may be.
The reason that I suggested that EliteKill try my Smarter AI module (and NOT my FULL Tweaks) is that my sneak changes include my Dynamic Stealth script, which reduces the perception/radar of the NPCs, based on time of day and the weather conditions . . . and this perception range changes even when you are not in sneak mode (although you'll still be detected much sooner while standing than while sneaking). Plus my Dynamic Stealth script uses different setting for interior stealth. It also makes Silent weapons a LOT harder to detect.
You also have to understand that Line-Of-Sight (LOS) in FO3 is horrid (after all, NPCs can see through buildings), so just hiding behind a rock or tree isn't going to work all that well.