Ever try to solder two wires together with little or no bulge in the splice?
I have found a way that works for me.
First I slide a piece of shrink wrap tubing on one piece.
Then I push the ends of two stripped wires together--end to end, so the wires are meshed. Then I take a single strand piece of wire the same size of the wires I am splicing together.
Then I wrap the single strand/piece of wire around the "wire bundle" and twist the ends so the bundle is pulled tight.
Then I solder the "bundle".
Then I trim the twisted wire end of the single wire off flush with the soldered bundle.
Then heat shrink wrap and DONE!!
Your solder method is a good idea.
FYI, we used to solder all connections with shrink tubing. Years ago, found a great manual compound crimper and with a box of terminals always found a 'better for us' alternative to soldering. .