If anyone is interested in more information on this subject, I have just found this article: “Selection and Use of Lavalier Microphones,” by Dr. Fred Ginsburg. https://www.school-video-news.com/index_files/Lavalier_Mics.htm
I think the article must be about ten years old, since it doesn’t mention the newest crop of lavs (such as the Sanken). However, it does provide a good discussion of the differences between “open” sounding and “closed” sounding omni lavs. I can vouch for some of what Ginsburg says, since the Sony ECM-50 was the lav of choice when I started in the business and I also remember when Tram revolutionized lav mics with it’s new, “open” sound that better matched boom mics.
Most interesting to me: Ginsburg thinks the Sony ECM-55 and ECM-44, the Countryman B3 and B6, and the Voice Technologies lavs are “closed” sounding, or what he calls “proximity” omni lavs.