As all the others have pointed out, your experience is completely normal. The more weight on the solid rear axle, the better off you'll be.
I've posted this before in a few other threads, but I'll relate my experiment with my BX on my hillside.
I was set up in full-dig mode. I had 265 lbs on the 3pt, 50 lbs in weights on each rear tire and about 90 lbs fluid in each rear tire, no spacers. I had the bucket on and down low, but at 23 degrees, it still felt tippy. I got off (carefully!) and went to the high side. I pushed on the ROPS with one hand and lifted the rear wheel. I went back to the garage, dropped the 3pt weight, took off the wheel weights and loader, then went back to the same place on the hillside. It didn't feel tippy. I got off again and pushed on the ROPS with both hands and could not lift the rear wheel.
The loader on the BX weighs about 400 lbs and much of that is out front. So not only do you have 400 lbs on the tippy front axle, but the amount of weight transferred forward due to leverage is also significant. Most people under estimate the effect this has on stability. Ballast on the 3pt is an absolute necessity, and it needs to be just about as much as the loader and contents.