The hardrock (like all MTBs and many road bikes) has a top tube which slopes back down, called a "compact" style.
This is designed to permit more clearance to your crotch, so you are supposed to ride with more seatpost extension than a conventional style road bike (with a horizontal top tube).

Even the slope of the top tube varies. Kona are known for having an extreme slope and are ridden with a lot of seatpost extension and a smaller "size" than other brands; its just their style.

You cannot compare the same size bike in compact style and trad style. If you need a 19" trad frame the you need perhaps a 16" compact frame.

The 19.5" hardrock is going to be too big for you. You need about 4" of space when you straddle a compact style MTB. The exact size you need is dependant on length as well as height so we can't guess.