Decathlete vault

[ttz]

http://youtu.be/B3N8xDiBQo8
Hello I'm a jr at a small college and we recently lost our jumps coach so I'm looking for advice. I'm a decathlete who started vaulting only for 2yrs. so far.
This is a clearance at 4.15m on a 14'0 175lb. pole from a short 5 lefts approach. I'm holding just above 13'grip in the video. The biggest problem I've been told before is my lack of bottom arm.
I am also 5'11 170lb so I feel my lack of bottom arm stops me from getting onto bigger poles which will give me more 'return'? Thanks guys!