According to Southgate News, someone has done some recent research. It would not surprise me if there was actually little difference! Funny how old wives tales become facts. Don't always believe what so called "experts" have to say.
Many said my own earth-electrode "antennas" in the ground would not work, but these have now been used from ELF-MF successfully and I am pretty sure at least one VLF grabber is now using such a structure. No, experts are often wrong. Always challenge! That is part of the fun of our hobby.
See http://southgatearc.org/news/2019/april/horizontal-versus-vertical-antenna-polarisation-the-debate.htm#.XMVi2PZFy00
This was a talk on the polarisation of 6m signals given to the Reading club. The link worked for me, even though I am not a club member.
https://groups.google.com/