Cranks are the metal bars that spin, with the pedals on the end.
They come in different lengtht, but most bikes have 170mm slapped on for a one-size-fits-all economy.
The cranks spin about the bottom bracket (at the bottom of the frame).
The layback of the saddle from the bottom bracket depends on:
1. The angle of the upright seat-tube of the frame.
2. The layback of the seatpost (which fits inside the seat-tube)
3. The length of saddle rail on the saddle.
Increasing the size of your frame will have no effect on saddle layback, only on the amount of exposed seatpost, which is irrelevant here.
The starting point for good positioning is to have crank length appropraite to your leg length, and the knee joint directly above the pedal when it is at the 3:00 porition. This is a starting point for fine tuning.
If you really do need to move your saddle back further, you can get seatposts with more layback. The clamping mechanism is set further back from the post. NB seatposts come in a variety of diameters, you need one which is a good fit to your seat-tube, or you may damage the frame.