Let's talk for a minute about who sets a "proper breed profile" style, or a show style. This applies to Bichons and all the breeds, really. No one person says, "it is this" Styles shift and evolve. The show style is a manifestation or reflection of how the breeder or show handler is interpreting the breed standard. Key individuals, usually outstanding handler/groomers or breeder/handlers often set trends. One person instrumental in the development of the Bichon Frise grooming style was Frank Sabella a renowned handler, who gave a grooming seminar to the Bichon Frise Club of America in 1969, which set the stage for the sculpted style of today. Mr. Sabella went on to judge the breed internationally at some of the most significant dog show events. Another breeder/handler who has been recognized as a leading stylist of the breed is Paul Flores, co-owner of Paray Kennels and one of the most winning handlers in the breed ring over the last 15 years.
The rounded head style that we see today has not always been the case. In the 70's, the ears were still distinct and the beard was left long.
The pictures above are from the website of Fountainbleau Bichons. Sometimes the bell head featured a more exaggerated beard. From The World of the Bichon Frise, by Anna Katherine Nicholas, I found this photo of Ch.Craigdale's Olé Rhondi, the top-winning Bichon of 1983.
The round head of today started appearing in the 1990's, first with the shortening of the beard, and then rounding the ears into the headpiece. Nowadays, it is not uncommon to see show heads that are actually a bit higher on the top of the head than long underneath. Bichon heads in the show ring can differ from week to week on the same dog, depending on the choices of the particular handler presenting the dog.
In pet grooming, the round head requires a lot to be taken off the ears. The owner has to be willing to give up the flowing ears. Way more than the bottom of the ears are trimmed; creating the "circle" necessitates cutting through the sides of the ears as well. Most importantly, there is no definition in front of the ears. The sides of the head are combed out to the ears, and only that hair that sticks out beyond the sides of the ears is trimmed. To avoid a heavy look to the face, it can be dished out a bit, and trimmed from outside corner of the eyes to the outside line of the circle. Cutting out under the ears does help to create a smaller, tighter circle, but can backfire if you cut too much.