Generally, a small 115v welder will do 3/16, but you have to watch your duty cycle. YES I SAID DUTY CYCLE
By your comments, you do have a good sense of what's going on in your welds. You realized you had to decrease stickout............which increases amps. I'd daresay that the reduced stickout started to occur, or was needed, the longer you ran the welder. I had a Hobart 140, and it did the same thing. Run it hard, and ya had to reduce stickout to keep the puddle good, and fluid.
Before we go any further............Lincoln flux core will run cooler than Blue Demon flux core. If you're pushing a machine to its limits, go with the hotter wire. The same can be said for stick consumables.......if you actually have a good grasp of what's goin' on under the hood.
Back to duty cycle...........the machine doesn't have to heat up, and burn to the ground, to see the effects of duty cycle. Most machines......the ones less than the "better" ones.......tend to produce reduced output as they heat up. It's not a big deal if you're aware of it, and either compensate, or take a break to let it cool down. I've lived with these small machines.
I can't weld like I used to, but I still have a fairly good sense of what's goin' on. You need to quit oscillating your gun............drag it, and gently weave it from side to side. Don't do dollops, or whip it. I see whipping in your beads.
I couldn't find plain ol' fillet welds on my pic files for 3/16 (probably got some on my backup drive, but that involves a bit of searching), but I found some cap welds that were done with 3/16 stock.........both the tubing, and the cap.

I like to take a square piece of stock for the cap.......same size as the tubing.........bevel the tubing....and weld the square piece to the top of the tubing. I then round the corners later. This was done with .030 flux core. Probably the same as you're using. Settings were in the range of a 115v machine............on the low end.
Anyways, back to the technique........................You can see that I drag the puddle, and I don't whip it, or try to make dollops. Anytime you go back into the puddle with this kind of wire, you lose the heat you're putting into the base metal......you're spreading your heat. Drag it, and keep it just ahead of the slag, or freezing leading edge of the puddle.....never go back into that puddle.....just drag it along.
I think you're on track.