Why not crimp THEN solder? Isn't that how some car audio guys do it?
That would only work if that crimp lug had an observation port forward of the crimp where you could insert solder. Do not apply solder to the wire side.
In any case, solder should not flow into a properly crimped connection. A proper crimp should have no spaces for anything to enter. Not even air.
The problem is that it is hard to identify a good crimp visually from the outside, and damn near impossible to get it on your first try. I suggest that as you're learning how your dies work with a particular wire/connector pair, make a few crimps, slice them across the crimp, file them down, and look at the cross section. It is important that EVERY strand inside the crimped area is deformed (usually they roughly form hexagons). Strands that are still round mean that insufficient pressure to cold flow the copper was used, and oxygen can still find it's way in. Also look for micro cracking of the connector, gaps in places, etc.
