I've been riding recumbents for years, but was a fairly experienced cyclist before that.
I've been thinking I might get back to riding a normal bike, and yesterday I was in a city a few hundred miles away from me where a bike shop selling an Italian brand of frames is located. I'd arranged for them to measure me up for a frame so that if I decided to buy one I could simply order without having to go back and see them.
The looked me up and down then sat me on a customer's bike (they said the customer was about my height). I was wearing office shoes. The saddle seemed really low, but they got me to sit with one foot at the bottom of the pedal stroke then dip my heel really low before saying the size was good and that I'd need a 55cm frame.
I remembered that my normal saddle height is around 780mm (BB to top of saddle), but they said that would be far too high, and sat me on one of their own (larger) bikes and got me to repeat the heel-dipping process. I couldn't dip my heel very far, and they confirmed I'd need a 55cm frame.
The measured the saddle height of the first bike at something around 720mm. They did say I might need to raise it by 10mm or so. After getting home I looked up some old bike-fitting notes, and saw my saddle height was 783mm (that would obviously change depending on cleat position, crank length and pedal\cleat stack height etc).
I'm open-minded, and realise common knowledge changes over time, so perhaps their fitting advice would be better for me. However, it does seem like a massive change, and because I wasn't able to pedal the customer's bike I'm not sure how it would feel. I suspect my leg position might feel a bit too closed at the top of the pedal stroke.
I know the old advice to roughly set saddle height was to extend a leg with the heel on the pedal, which would then give a bend in the knee when pedaling. However, I'm curious about the heel-dipping 'test' - is it a new thing, and what does it do?