I need at least 3 additional MOA out of my scope.. @ 100yds
Has anybody added shims to correct this and if so what additional height would be a good starting point???

You can get brass shim stock from machinists suppy shops.
Depending on the scope and your ring height, it might take between 14-18 thousandths.
Bear in mind, if you raise one mount much over .010", you should "lap" the rings after adding the shims, to reduce "flexing" of the scope body.
Of course, you might just disregard this info, some "guru" should pipe up soon.lol

What action, base, and rings are you using? Also, what caliber? You could rebed the scope in JB weld if it is a light kicker, but since everything varies from one design to another we really need the other info.

The problem that will most likely occur if you shim how you are thinking is that it will bend the scope. Not knowing anything else I would suggest getting an aluminum one piece mount and sand/grind/machine that.

Whoa I just read your problem again, what are you shooting, a 22 short?!? Sounds like something is mismatched or else a wacky scope.

Just for grins you could try rotating the scope upside-down and see if your missing elevation reappears.

No nothing is mismatched...
Sendero 7mag
Leupold Dual Dovetails (Reversable)
Elite 4000 6-24
I have ring alignment rods
And this is the second rifle this scope has done this on - the other being a 7mm08 VLS
that had regular Leupold mounts..
This scope had plenty of vertical when on a Ruger 77 Hornet varmint and on a custom flattop AR15 in Mark IV Rings..
The scope clicks are 1/8 min.. and work in every direction fine and the point of impact is the same at all power settings....
I went to the Reversable on the long action thinking the spaceing might help - I think in the
A.M. I will Measure ring difs and spin them and
or change them front to back to get the rear up and lap them at a dif.. angle.
Shims = 5.95
20 MOA bases and new rings = 75.00
See why I asked for a shim height.....

The easiest and best way to do this is to go with Burris Signature rings. Once you have those rings you can either get the offset inserts or you can just shim the base. Those rings will not stress, bend, or kink the scope tube at all, even if you shim the base.

As far as how much correction you need, the rule of thumb is .001" worth of shim equals 1" at 100 yards. Therefore you would need a .003" shim. Keep in mind however that a scope "works better" when it is in the middle of it's adjustment range.

If it where we, I'd do this: take back or sell on Ebay those Leupold rings. Buy the Signatures in the height required. At the same time, order the offset insert kit. The rings are just a few $$ more than the Leupolds and the insert kit is about $16.00. Now determin the center of the scope's vertical and horozontal adjustment ranges. Use the front ring and the required inserts to correct the elevation and use the rear ring and insert set to get the windage perfect. (I know you didn't mention a windage problem, but you may as well get that perfect also while you are at it.) Tighten, and you're done.

Those rings will hold a scope on just about anything you can fire from the shoulder, and as an added bonus, they will never mark the scope tube.

If you still have questions, Burris has a rather good explanation on their website.

Gabe