True, but sometimes the hole in the bead is too big for a smaller fly. I most times use a properly sized or one just a little bit larger and wrap some lead wire (or lead substitute wire) around the shank behind the bead to add weight. The wire also locks the bead in place against the eye, making it a bomb-proof fly. In fact I call them my "bomber" flies. You can use different diameter lead and/or wrap more or less on the length of the shank depending on the size of the fly or how heavy you want to make your fly.Sometimes I run heavier beads on smaller patterns, so not really proportional, but useful when I have to get a relatively small fly to sink rapidly in cold/dense water.
I have never tried floatant on nymphs, ingenious!Add some floatant to the nymph and you can fish it as an emerger. This "kills" sometimes.
That's the great thing about tying your own flies, you can tie flies for different conditions rather than having to fish whatever you find in the bin of a fly shop or buy the flies find online.
I always wondered. You tie a nymph to an exact pattern to resemble the real thing. But nymphs don't have silver or gold or red heads