Hi Oleg,
What you are trying to do goes against grain of what DITA was invented to achieve. 
DITA was invented to allow authors to create reusable "chunks" of content that could be referenced across many map files. It seems that you are authoring your Topics for a single map file. Will there be no reuse of the Topics across maps? If so, saving them to a folder with the map could be confusing for users down the line and you may inadvertantly have duplication.
Further, regardless of your use case, you don't necessarily have to save it in the same folder as the map. An easier approach for navigating to related Topics is to use Windchill's Structure tab for any given Map file.
When a map is bursted into WC, links are created between the map and all referenced Topics. You can see a list of the referenced Topics from the Structure tab and it will link you any of those Topics information pages.
You can continue to save the Topics in a general Topics folder as you have described and the Maps in a different folder. Then users only need to find the Map file rather than scrolling through a folder of Topics and subfolders.
Hope that helps!