I am not sure the reasoning for the support in the middle of a tri-arch, but it just does not fit in my opinion. Great job on coming up with the new arch options though, I love them.
Here is a picture of a T-arch with a fence, if this was to be a fence gate it would not make sense at all. Even without a fence gate and just a regular fence, it does not look like a good match in any case.
The right and left arch's used alone look great, and I see no reason why we can't have a center arch without the post in the center, call it a crown arch, as I would like to use a tri-arch in a few designs, but will not if its an area I want more open without a post.
Please change the T-arch or add a crown arch.