It is not uncommon for those new to Crimson to overlook that the source address is a word address, not a bit address, and this includes B files and flag tags and so they miss the next step. Skip it and it won't work.
If you want to see bit B3:0/0 then after you choose B003:0000 as your source you must then set the Treat As parameter from "Unsigned Integer" to "Bit Array Little-Endian" and then set the bit number. Otherwise the flag tag is going to use the integer word B3:0 instead of the bit B3:0/0.