I've been wearing a topper since 2009 and over the years, my growing hair in the back has continued to thin. So much so that I ordered two new pieces with larger bases to cover the thinning spot. I know this should be a simple thing to do, but I am nervous about accidentally shaving off too much hair in the back to fit my new pieces. Any tips, advice from those who have gone to larger bases and how you were able to shave the growing hair, but not too much?

Thanks
John