Iceman the elbow should travel in as direct a path as possible from guard to its target and back down the same path, basically dont flare the elbow on straight punches, if your flaring elbows you will see that the path the elbow follows to full extention will be quite a strange curvey path rather than a direct path, this isnt good economy of movement and aswell like i tried to explain it leaves greater potential for force to escape from joints due to the weaker muscles being the ones supporting the shot, this is mainly a problem when having range messed up, range being miss judged or timing wrong or the shot gets smothered, whatever can happen in the ring, elbow traveling in a straight line gives the joints of the arm support from the strongest muscles, is a lot quicker as its a more direct path thus wastes less energy and gives greater potential for a stronger shot through a larger range of motion of the strike.

Hope this makes sense now lol, i just like to explain why good technique is used it helps me work things out in my mind and sometimes writing it down helps me think things through in more detail, itll also teach you a principle to use and why to use it rather than just help you with one specific punch your having trouble with.