B16x2 Keyboard is comprised of [16 key + 32 key]. You can use 16 key in a small screen or at first. As it goes, however, you had rather utilize 32 key. It has the optimization for human hand structure which can never be reached by qwerty.
It can be different for each person or device. So otherwise you need to find your optimization first by adjusting button size, etc. to be the most comfortable for you. Then your thumbs can fly like a swallow.
If you are familiar with 16 key, you can naturally do with 32 key. At 32 key, put gravity on center two columns carrying first letters of 16 key and slightly move outward for edge columns.
From this you can see the future keyboard you can type fast in a consistent way anywhere from mobile to desktop.