I just tried a 2.3MM tungston bead on a Tiemco 900BL in 16 and 18's and got no slippage. The 900 is similar to the 100 so hopefully that helps you. These are nice, very small profile beads that leave you ample room to play on small hooks and get the fly down with the tungston.
Do not feel to bad. At least you figured it out while tying the flies. I had a batch I did this winter that were so close the bead came loose on the first two, while fishing this past spring. I did not notice while tying it was so close. A batch of thick head cement back at camp seemed to fix the trouble so the flies could be used the next day. Worked long enough till I lost the flies to fish or they flies were to chewed up to mater to me that the bead was gone. It was time to change flies any ways.
I like using large BH on a small hook. You can put the BH on the hook last instead of first. Also, it lets you put more wt on the hook which is why one uses a BH in the first place. Simply tie a piece of tinsel near the hook eye. Slide the BH onto the hook and tie down.