Rear wheel spacing on 650C bikes

[Veloo]

I've seen some 650C road bikes with a lot of spacing between the rear wheel and seat tube.
Here's one example.
https://sevencycles.com/7/wp-content...Greenfield.jpg

Then I see some that look like a normal road bike like this Norco.
https://www.velominium.com/en/produc...ence-650c-2019

Is there any particular reason for the extra spacing?
When I first saw it I thought it was a 700C frame made with 650C wheels but the pages/ads say the frame is indeed a 650C one.

Is it to ensure heel clearance of the RD?

[Mark McM]

It's not necessarily a question of purposely leaving extra space between tire and seat tube, it's more a matter of desired chainstay length, and also seat tube angle. If a road frame was built with typical road bike chainstay length and seat tube angle, but it used 650c tires instead of 700c, there would just naturally be more space between tire and seat tube.

For whatever reason, the designers of the 2nd frame choose to use short chainstays. Perhaps part of the reason for using 650c wheels was to allow for shorter chainstays. (The main reason that smaller bikes often use smaller wheels is to allow more freedom for in small frame design.) But it should be noted that most derailleur drivetrain manufacturers will spec. a minimum chainstay length (usually around 39 - 40cm), and it's possible that the short chainstay 650c bike actually violates the chainstay length minimum.