Having issue with 20 gauge sheet metal and MTS251Si

Hi,
I am having a little trouble with my new MTS251Si. I am using .025 wire. We have dialed it down t0 15.5v and 128 wire speed. I have had a hard time maintaining an arc and it appears a fresh tip will help for a little while, but then it starts to sputter again and won't maintain an arc. Changing the tip will fix the issue for a while.

The other issue is that there seems to be a good deal of play with the wire in the liner. With the gun off, I can move the wire in and out about 3/4 inch. Is that too much?
Would a 24 series gun be a better choice for the smaller .023 wire and .030 wire that I use for sheet metal?

I bought this machine to do larger projects as well, but my understanding is that it can run this smaller wire. Any thoughts or advice? Thank you.

We figured it out. The tips that I purchased were not very good. They would not last. Once a better brand of tip was used, we had success with the small wire on sheet metal.