A 9" BG @ 9 oz. that you have caught is 112% RW. The bass that you are catching @ 7.5"-9" can only eat BG that are 2.5"-3" in length max. The LMB in the pond might not have enough cover for them to ambush the BG from, so they might be like marathon runners, constantly swimming and burning up calories to catch enough BG to survive, let alone get fat.

The biggest BG are most likely the ones that you stocked, just like you are thinking.

I'd look at transferring LMB that are between 1# and 2#, I am not sure that larger fish than that would do well in the pond since they are used to catching fish to eat in the BOW that you sourced them from. Bob Lusk stocked bigger LMB in a clients pond and found that they actually lost weight ( maybe because they couldn't figure out the best places to ambush forage fish?). Those 1# to 2# LMB would be eating BG that are (roughly) between 3" and 5.3" in length. Don't a lot of LMB that size, just a few, and I would fin clip those particular fish to allow you to see if LMB that size are caught whether those fish were stocked by you or if they grew to that size in the pond.

I didn't see if that pond is aerated or not. If not, during the summer the fish probably won't be able to utilize the water that is deeper than 8' due to low O2 levels.

Another thing to think about is that you need cover in the pond not only for the bluegill but for the LMB. The cover for the LMB has to have openings in it so the LMB that you are wanting to thrive in the pond can swim in/under, turn around and face out to ambush prey fish that swim past. Ideally you'd want to have roughly 20%-25% of the surface area of the pond in cover for the fish in the water depths that they will be able to survive. Depending on the water temp in the pond during different times of the year that may be shallow water or the deepest water in the pond.

It looks like you are just measuring the length of the majority of the fish that you are catching. Make a chart for LMB and another one for BG, get a good scale and record both weights and lengths. That will tell you how the fish are growing, and if a certain length of LMB is under performing (as noted by weight) that will tell you about what available food sources that size class of LMB has to eat. You'd want to cull that size LMB and the next size smaller to allow the available forage fish to grow larger to feed the size class of LMB that is underweight.

If the goal in the pond is to grow big BG, then cull any LMB over 14". If the goal is to grow larger LMB (that will be hard to manage in that size pond) I would recommend culling the smaller LMB and fin clip 50 of the bigger LMB and only leave those fin clipped bigger ones in there. That will also give you an idea if the bigger LMB are getting hook shy (record the number of times you catch a fin clipped LMB and note any identifying marks on the individual fish).

You could buy a fish tagging kit with numbered floy tags, that way you could track the individual fish length/weight if re-caught.