GCF ... you'll get a little more back meat if you angle your cut a little more above the eye of the fish, then roll your blade tip & continue your cut down along the backbone. You won't be losing anything of interest, in the belly region of the fish, by angling the knife blade more towards the front of the fish.

I make a elongated S cut ... starting almost above the eye, then around the gill plate, and into the stomach area. I'm basically doing to the back/shoulders of the fish, what you're doing with your stomach cut ... opening up a easier path for the knife to follow. Once I've made the opening (S) cut ... I put the knife back into the incision, and turn it towards the tail & cut along the backbone, keeping the blade tip alongside the top ridge of the back & next to the dorsal fin. I don't worry too much about whether or not the knife blade is under the belly/rib section ... until I get at least to the middle of the fish ... as I'm disposing of that section, anyway. But, my main point (to you) & my main focus when cutting the fish, is to not sacrifice the two thumbnail sized chunks of back meat (over the eyes), in favor of a quicker/easier cut.

You can easily see the difference in the size of your filets ... if you cut one side your way, then the other side my way, and compare them side by side.

... cp