No matter what the science is, you can reduce the burping by using a modern feed as Brian recommends, but it does not totally eliminate it. My FPN Passoporto still burps when ink levels are low. You can also reduce the volume of the barrel. I have done this with my ebonite Indian eyedroppers by adding beeswax to the barrel (drip it in from a burning candle and then put the barrel into water that is almost boiling to liquefy all of the wax and let it cool) so the volume is halved, which still leaves you with a large ink capacity, but an even lower probability of burping. With the Indian pens, I have also sometimes used a modern NoNonsense feed with the wax trick to almost totally eliminate the burping.
By the way, burping sounds kind of quaint, but if you are sitting in a meeting, and several large drops blot onto your notes and gets all over your hands, it is not fun.