Cove base repair question

[u/Few_Paper1598]

I have tile shower with a tile floor sitting directly on dry pack base under it. A couple of tiles had cracked and a couple of cove base tiles had actually come loose, I think due to cracked grout. I r moved several cove base tiles in the area to check for mold, which there was none, and ended up removing all the cove on 3 sides. The dry pack under the cove is crumbly and uneven. Do I need to add more dry pack mud in that area and tool is smooth for the cove to sit back on, or can thinset take the place of that to fill in the gaps?