If you genuinely want to shorten the "Reach" of a bike frame, to be shorter than what is already achievable on say a 42cm, 700c wheeled bike, then the ONLY option is to move to a bike frame that uses smaller wheels.
There is no other option as its the wheel size that limits the lowest possible "Reach" that can be specified.
Your looking at 650c (ERTRO 571mm) or even 24" (ETRTO 520mm) for narrow high performance tires but if you want wider tires your looking at 24" Mountain rims (ETRTO 507mm) or there are some wider options for 24" (ETRTO 540mm) available.
Short top tube lengths can be achieved on spec sheets with 700c wheels simply by making the seat tube angle steeper but this doesn't shorten the "Reach". If you really want a bike with a genuinely shorter "Reach" then there is nothing for it except smaller wheels.