Is the tail spinning at maximum RPM? If you give it right stick to try to stop the spinning, does the tail spin any faster? I suspect not. I think you have maxed out the tail motor.
Shortening the tail boom reduced the mechanical advantage of the tail. The tail motor has to work harder with a shorter tail boom. Try using a stock length boom to see if the EDF you are using has the physical strength. If it does not with a stock length boom, give up. That EDF will not work under any circumstance for you.
And for ballancing, do not try to change the mechanical setup. Instead, try moving other componnents. Push the batteries further forward. Push the receiver forward. Use your 3 cell LiPo instead of the 2 cell. 3 cell LiPo will help with balancing, and give the tail motor more RPM.
EDF is Electric Ducted Fan. What EDF unit are you using?