Actually, what you will notice is that with the better Yurchenkos, the gymnast's hands will be closer towards the front "dip" or "curve" of the table. Typically, they're right on the "curve" or at the top of the curve.
If your gymnast's hands are in the middle of the table, then it sounds as though she's coming on too high. Now, the question arises as to why she's coming on too high? In most cases, this can be related back to the hurdle and the round-off. Something relative to those two skills is breaking down such that gymnast has an insufficient turnover and is not in optimal position while in contact with the board and just prior to take-off.
With a less ideal board position following the RO, typically the gymnast will sort of be performing a "gainer" onto the table. This results because the center of mass will end up either directly above the feet or possibly in front of the feet slightly (if the chest is down a good amount) due to the insufficient turnover. This affects the amount of rotation (torque) that can be generated from the board and causes more of a "gainer" effect because the gymnast must "throw backwards" in order to get to the table as opposed to just reaching backwards.
As far as the angle once upon the table, I typically observe that the better Yurchenko vaults will create an angle of between 45-55 degrees from the hands to the feet relative to the left or right horizontal (depending on which side you're viewing on). Of course, the gymnast is in a stretched (hip and chest extension...possibly slightly hyper) position during the support phase...or at least they should be for the most part.
Another issue that may be occurring is that due to the possible gainer effect as I am hypothesizing, the head may actually be leading backwards. If this occurs, the arms will never catch up. As a result, the gymnast will be "planching" in the support phase. Obviously, this does not make for a strong blocking position. As a result, the gymnast will usually start to tuck/pike (layout...which usually ends up being a semi-pike position) early. This will also cause them to end up closer to the table.
So, take a look at the front side of the vault. Shoot some video and compare it to some of the better vaulters in the world...in particular, I really like Cheng Fei's technique. I bet that you'll find some of the things that I'm saying to be true when you start looking at the film.