I used a red coloured scotchlok, that is 22-16 AWG on the back of it, perfect fit. the blue might be a bit big indeed. I really don't think it's worth soldering. This is creating unnecessary work and making it a permanent connection. With the scotchlok it's easy to remove the kit if you ever need to without leaving a trace.
The scotchloks doesn't create enough force to slice the wire nor is the blade part of it small enough to do so, it barely pierced the insulation for me.
What i did though, i stripped some of the headlight loom sleeve keeping the scotchlok away from the connector block for the headlight incase needs be that the cable needs to be joint together, there is enough room for a crimp