Hi Dave,
You definitely need to be scraping over a rounded surface like an old drainage pipe or very smooth log about 6" diameter. The soaking will tend to make the hair 'slip' in some places more than others. Also, deer hairs are very prone to breaking and shedding everywhere if used as a rug so it's better that you get them all off anyway. If I were you, I would scrape all the membrane and flesh off over a rounded beam and then put it back into soak in a water and wood ash solution for a couple of days, then just 'push' the hopefully slipping hairs off with a fairly dull blade again over the rounded beam or pipe. Then follow all the usual steps for producing buckskin. Or you could stretch it in a rack and use your right angled hide scraper to remove the membrane from the skin side - I do that quite often but you need to be careful how much weight you put behind your metal edges or you could go through the hide fairly easily.
If you want to keep the hair on a deer hide next time (for a wall hanging?) it would be best to scrape the flesh off when it's fresh (or put it straight in the freezer if that's not possible) and then stretch it out on a rack to dry scrape the non hair side before braining, working, drying, buffing and smoking. Try not to soak it at all, just dampen it on the skin side only when required.