Joining placket bottom pieces neatly

I’m working on a top-down sweater with placket front, the 8-stitch wide placket is worked in garter stitch. So far so good. I’ve joined them before by moving the stitches from one end to another needle and working the 2 sections together. My problem is that the last stitch of the placket next to the stockinette of the sweater front is always big and messy. I’m not sure why. I’ve tried slipping a stitch on both placket sections but I didn’t get the desired result, it still looked messy. How can I avoid this? The only solution, if you can call it that, that I’ve come up with is to either work the extra yarn out by distributing it out into other stitches or pulling it up and securing it with yarn on the back. Neither makes me happy. I expect there is a better way. I wonder if working a decrease on the last 2 stitches on the underneath piece on the row before joining the might help. (Does that make sense?) I guess if I did that I would need another stockinette stitch in there? Any solutions?

I think that twisting or knitting into the back of the first garter st after the st st will tighten it up just enough to avoid the looseness. You can do it both on the RS and WS, but see if maybe just doing it on the RS will help.