Small peppers even left whole would sink with 2 small slits cut into them. That is what the instructions are assuming.

But you are using quite large peppers so you can either do them in 1/2" slices, larger chunks. Peppers that large really shouldn't be left whole. The salt water and the brine both have to have ready access to the insides for both flavor and safety. Floating won't do it. But if you want to leave them whole then you'll need to cut several more slits in them and then weight them down in the soak with a plate or such.

Personally I would stem and cap them (leave some seeds for flavor) and then cut them into large bite size chunks. Peppers that large will be difficult to put in jars. But how you cut them all depends on how you plan to use them later.

Dave