Yokozuna Reaction housing question

[David in Maine]

Trying to replace the brake cables and housing on my bike with Shimano R8000 shifters and TRP Mid-Reach brakes. Switching from Jagwire compressionless housing to Yokozuna Reaction. The diameter of the new housing is larger and it doesn't seem to fit into the slot in the Shimano levers. The Yokozuna kit came with step down ferrules, but they don't really fit either. What is the correct way to do this?

David