Hi Jeffrey, thank you for your quick answer. But your idea is not the solution for me. The expression should look like the right example, more compact without this ugly gap. Maybe someone knows a solution for the problem.
Lothar you will have to create it but it can be very simple and no special hoops to jump through.
Copy the sf marking so you now have two of them. Select the f marking and ctrl-c it. Now simply paste, ctrl-v, the copied f to the end of the new sf. You can even change the size of the second f if you so choose.