[Converting to CMYK - blacks go to k=100 rather than a rich black.]

In a further test, I was able to make an acceptable CMYK file by exporting an RGB jpeg from Affinity, opening that file in Affinity and converting to CMYK. That result is also attached. It's not the worst workaround, but a little weird. 

Fantastic_Four_Stores_-_front.afphoto

Fantastic_Four_Stores_-_front_-_bad_cmyk.afphoto

[Converting to CMYK - blacks go to k=100 rather than a rich black.]

The shadow is not a vector object, everything is a pixel layer. I'll know next time to build the file in CMYK, but I'd like to figure this out too. Converting with various other profiles makes no difference either. 

[Converting to CMYK - blacks go to k=100 rather than a rich black.]

Attached are two screenshots. The first is from a RGB JPEG file converted to CMYK within Photoshop with US Web Coated (SWOP) v2. The second is the layered file I made for the project in RGB all within Affinity Photo, then converted to CMYK with the same profile as Photoshop. The black part of the design converts to C=0 M=0 Y=0 K=100 when converting in Affinity and C=75 M=68 Y=67 K=90 when converting in Photoshop using the same profile. The rich black in the Photoshop converted file is what is desired, but why the difference in colors, and how to fix?