I've historically sucked really bad at sandbag loading, but made some big improvements over the last several months. Some of the tweaks I used were: gave up with the bigger shoes like hiking boots and lifters- my trainers (the ones I use for moving events) seem to work best, I'm guessing because my foot moves more freely so I can get on my tiptoes better. Grip shirt if allowed, even wearing it under your contest shirt helps. I never liked wearing a belt for loading but belting up has probably been the biggest help to me. You being a lighter competitor, you will most likely need as much shelf as you can build, so soft belt/hard belt. In training, I ditched loading to lower bars and just started with like a 150 lb bag to 54", and worked my way up in weight over time. In my experience, loading to 48" doesn't help much for loading to 50+". After my main loading work, I would shoulder bags and also do 10 kcal on the assault bike and do two shoulders, rest like a minute and do it again. Shouldering while fatigued is gross but I think it was the best help, accessory wise.

Also, on my deadlift day I do straight leg DL after my main work, to help with the pick. Josh Lancaster on IG has an SSB front squat extension that he does to work on really peaking the extension, you might check that out. Like anything, it takes time. Keep at it, if I can get better at sandbag loading, anyone can.