Originally Posted by RobotGuy

Like mcourse said above... you’re probably missing the 16T or possibly the 18T. So In that case, moving from 11-28 to 12-28 might just work for you.

Are you ever desperately in need of that 28T cog? If not, perhaps you could buy the 12-25 and have even better resolution where you need it. If you stick to the exact brand and level cassette, you could always swap the 28T back in.