The problem is that a regular suit jacket or sportcoat just is not cut correctly for wear with a kilt, they are too long and make the wearer look as if he is a child playing in his parents closet, I am sure this is not the image you wish to project, a properly made kilt jacket is not just shorter than a suit jacket there are subtle differences in the pattern.
If you are not comfortable with the more traditional look of the argyle jacket for example there are more modern choices available these days, if you look for them, if you are on a budget there is always the option of getting a coat from a thrift store and converting it for kilt wear there are many examples on this forum, look under the Do It Yourself section, and