Ok so i have a couple of tips...

But remember this is not horrible..Im sure you wont think it is.. Think of it as constructive criticism

First your guard..You have a good gaurd.. You are like me ..You keep it high!

You keep it so high that when you throw a jab it comes down when it is fired strait..

Instead of having your hands at your chin and firiing it out totally strait so that when your arm is fully extended your chin is tucked in behind your arm.. You have your glove up by the side of your head about paralell to your eyes or forehead..

You also dont bring your jab back fast enough to guard..

So the first thing to work on is the jab.. Try to quickly lower it slightly before you throw a jab but dont bring it away from your face..And dont make it obvious..

Then once you fire it fire it strait while remembering to keep your chin tucked in and once your jab is extended fully, your chin should be tucked away behind your jab..

Now.. Another thing is your range.. You are walking in with your hands up to get in range to punch him.. Now this has been ok for you because your partner seems to be fairly inexperianced also..

But if your just walk in with your guard up ..yes you are getting into range for your shots..
But with your partner bieng so tall you are infact walking right into his range before he is in yours..

Practice your speed.. And your jab.. Try to snap your jab out..
If i try to explain this in a simple way it would be that you throw your jab out strait,relaxed but yet as fast as you can.. and just before it hits..whether its the bag or someones head..

Turn your fist in the last few inches or so and tense.. I will try post some simple video's of this maybe tomorow if i can steal a video cam..

And with this new and improved jab.. Work on stepping in with your punch..
Your stood on the ball of your right foot..And when your step you push of hard on the back foot and step in with your front foot and throw the jab at the same time.. Double the jab..

Aside from the jab.. Its just the commitment to your punches..

I can tell you have thought about this quite often... How hard should i hit him.. How do i fight such a tall guy.. Its this thought and unsureness that is effecting your sparring..

Commit to your punches..want to hit him.. Be patient..

For example.. Your right.. You throw it good at times.. But at others..You throw your jab and then just put your right hand out there with no commitment...

Try firing your improved step in jab..And turn in with your shoulder and try the same snapping motion with your strait right hand..

I have babbled to much for now.. If it is of interest to you..And you would like me to post a vid or two dont be afriad to ask..If i lost you a while ago and i am not helping you then do not worry about hurting my feelings and telling me to piss off :P Lol..

But i hope this helps somehow :P

Bodyhead