The shit sandwich is a tool used because you feel the person isn't capable of handling direct criticism.

When using the shit sandwich on a senior report, you are implicitly stating that you don't believe they can handle direct criticism.

I'm not in a senior position and I HATE getting the shit sandwich, it's irritating and insulting. Most of my coworkers (in various positions of seniority) also hate it.

I wouldn't use it period, unless you know for certain the specific person cannot handle criticism.

Senior employees want to take action, solve problems and get on with things. Sugar coating it is wasting both people's time essentially. At least that's my understanding from the context and my personal experience.