The problem with your measurement is that you've marked the top tube not the seat tube. BMX frames are sized by top tube length but others are usually sized by seat tube length. As your problem is leg extension it's the seat tube you should be more concerned about, although you can fit a longer seatpost to a smaller frame to get correct leg extension (most cheap bikes have short seatposts). Then top tube length and stack height determine the starting position for the handlebar, which you adjust with stem length and height/angle, and bar rise, sweep and width. A classic road bike frame has similar seat tube and top tube lengths, but mountain bikes and cruisers tend to have seat tubes shorter than top tubes. I have road bikes with 25" frames and mountain bikes with 18" frames, set up so the riding position is pretty similar on all of them.