would it be possible to build a g7fek antenna wth the windowline running horizontaly,would that be better for nvis?
all is possible, you can modify it as you like, but before doing so, maybe, just maybe, it could be the case to understand why that antenna was designed that way and how the currents flow on it, otherwise I strongly suspect you would be condemned to a failure to achieve what you want
anyhow, go on and modify it, call it as you want (since it won't be a "g7fek" anymore) and have fun