I don't have access to a Pro Mig 135 and have never used one so I can't tell you what to set the dials on. I can tell you what I would do in general.

It sounds like you want to increase the penetration of your welded joint. With 14 gauge material it will be easy to burn through but you can try several things. Keep in mind that your adjusting should be gradual and controlled so that you know what differences each change made.
1) You can increase your fit-up gap a bit and maybe use an aluminum back up bar on the other side.
2) Increase your voltage.
3) Decrease you wire feed speed.
4) Travel faster and maybe even incline your plate so that you are welding upwards.
5) Use a combination of any of the previous 4 items.
6) Weld both sides instead of just one side.
7)Set your joints vertical, turn up your volts and amps, and run downhand. (This can be tricky though, and it doesn't sound like you need to try this unless all else fails.)

By holding a 1/4" ESO instead of 3/8 - 1/2 you decreased the current and increased the arc voltage a small amount. That made your tacks penetrate and flatten out. You want to do the same to your welds except that holding such a short ESO will cause more spatter to get into your nozzle and everything will get hotter. It will be harder to see the joint while welding and you might end up putting your contact tip or nozzle into the weld. I would turn up the volts and turn down the wire feed as I mentioned above. Again, make gradual changes.

I wouldn't say higher wire feed speed "magnifies" the heat. It does increase amperage if all else is equal, which means more metal is melted. If too much metal is "piled up" in your bead you will actually insulate the base metal from the arc and limit your penetration. Plus, you can get slag entrapment and other nasty problems. Generally you want to stay on the leading edge of your puddle for penetration. For reduced penetration, allow a little of the puddle to get ahead of the arc.

I don't know if any of that helps or not, I hope so. By having a little "play time" I'm sure you will get the results you want.

Chet Guilford

I have always repected Mr. CHGuilford's posts, and this is kind of awkward, but.....

From all the manuals I've seen and personal experience, with a CV power source, a shorter wire stick out increases the amperage. A 1/4" to 3/8" is the recommended electrode stick out for short cuircut GMAW. 1/2" is a little long. The longer electrode stick out decreases the amperage,
making the puddle cooler. From your own observations, the shorter electrode stickout gives you a "nice circular shape" and the longer electrode stickout gives you "Mt Everest".

With short ciurct, the voltage and wire speed should always be adjusted together to provide the maximum number of "short cuircuts". This is that smooth buzzing sound, and will produce a vertually spatter free weld. On your machine, I think you have to adjust the wire speed, because the voltage is set in ranges. Increasing the voltage also means increasing the wire speed for a stable metal transfer. So, running "hotter" also means traveling faster. It also produces smoother beads. For the small welds you trying to make, run as hot as you can handle the travel speed.

Mr. Guilford did mention leaving a gap. Try snipping off a short piece of welding wire, bend it in a V shape and use it as a spacer between the two pieces. Tack one side of the pipe, pull the spacer, make sure the gap is uniform, and tack the other side. Check the gap again, and put in two more tacks at the quarters.

Penetration is really controlled by where the wire is directed onto the puddle. As Mr Guilford said, the lead edge for penetration. If your burning through, you can push a little of the puddle in front of the wire, but not too much. If you carry the wire too far back, you can actually float the puddle right on top and not tie in at all.

Don't angle the gun too much. As your going around a piece of pipe, keep it aimed at the center, maybe angled a little. If you angle the gun too much, you end up with a longer electrode extension.

Use 75/25 shielding gas. The increased amount of CO2 provides a more energized envirement that helps break up surface oxides and allows for better penetration.

If your penetrating half the thickness of 14 gauge, around the circumference of a piece of pipe(tube), it's uniform, and you can't break it beating on the concrete, for your application, your probably doing ok, unless you intend to grind the weld flush.