These are problems that occur sometimes - the change in playing standing up compared to sitting down and the change from playing through an amp and not playing through an amp. To get around the standing up sitting down issue I always play standing up. You gotta know that if you play sitting down for any length of time when you try to play standing up and with a strap it's going to be different. Why not just pick one and the obvious one has to be standing up due to the playing live. As to playing through an amp (because of things you don't hear without it and harmonics and distortion and all the rest of it (and i don't necessarily mean dirty tone all the time, just through an amp)) I haven't solved that problem because i'm in a ****ty apartment and people can hear you when you .. do stuff.

I haven't played sitting down for a couple of years. Although I guess i could because I play my guitar high enough that it wouldn't make a difference if I sat down or stood up ( the guitar wouldn't be resting on my leg). I lied as i've sat down twice to find that fact out.