Scooby, 

First, I don't think you meant 2ipm.  That would be awfully slow, even for Short Arc. 

Second, at what angle are you running your gun?  You asked about changing it but didn't say how you were holding your gun.

I could start with a long description of how it should be done, but you can find that in many books and in other threads here.  Check the search function for past threads.  However, a quick answer probably needs a couple answers to the above questions.

Others may join in and offer suggestions that will help.

Have a Great Day,  Brent

Scoob

A 1/8 land on half inch plate is pretty thick for short circuiting GMAW...  You could go down to about the thickness of a nickel and be fine.

If a 1/8 root gap is working for Flat and Horizontal, it might be apropriate to slim the gap down to 3/32 for Vertical with upward progression.

Try between 170 and 200 ipm  17.5 to 20 V   Inductance to max for open roots.

Contact tube should extend 1/8" beyond the end of the nozzel

Gun angle should be 5-10 degrees push..   What often happens is that the welder will have a perfect gun angle for the first half of the weld, then as it gets a bit harder to see as the weld goes above eye level, the welder will tip the gun angle a little more so see better.  That small change in gun angle will cause a reduction of penetration and may even increase the opportunity of the dreaded whisker.

Just remember, You may have to run a relatively low wire feed speed on that open root (165-170 ipm)...  You need to make an increase to weld out the filler passes.  Short circuitng GMAW is not well suited for half inch thick steel... It can be done but it takes a pretty high level of skill and process control.

Open roots are alot cheaper to practice with palin old 2"x6"x 3/16" carbon steel with a 1/8 to 3/32 root opening  :)

Follow all Lawrences tips and also, try to put just a ****hair bigger gap at the top of the plate then what you have at the bottom.  Your gap closes shut as you get closer to the top.  I put my roots in with a 1/8 gap, 1/16" land(root face) and run around 15.5 volts and just around 200ipm for vertical.  Overhead is 1/8" gap, 1/16" land, 16v and 220 ipm.  Flat and horz are 1/8" gap, 1/16" land, 16v and 215ipm.  There are a number of gap, root face, voltage and wire speed combo's out there, you just have to find what works best for you.  Gun angle is a huge factor when putting these roots in and will throw of your setting considerably.  So in other words, find a gun angle that fits your style and find the gap, land, voltage and wfs combo that fits your style.  Contact tip 90deg to the plate= more penetration.  The more you drop the gun angle, the less penn you will get. You will have to use more wfs and voltage to punch her through if you run a tilted gun angle.  I run 90deg to the plate wherever I can and rock the gun back if it looks like it's starting to punch through a little to easy.  Hope this helps ya some.