There is an insertion tool for Powerpole connectors. Go to: https://powerwerx.com/powerpole-inse...xtraction-tool
I found that the tool sometimes helps when direct force on the wire isn't enough. Sometimes.

As for tinning the wire before crimping, my experience is that manufacturers of crimp terminals recommend against it. If my memory serves me correctly, the solder will flow under crimping pressure and negatively affect the wire to terminal contact. Bottom line is to not tin unless the manufacturer specifically says to do it.

--Bill Mc