So I finally did a thorough measurement of my hair. I put my hair into 15 plats on the top and 9 cornrows in the back where my undercut was. Most of my hair in the undercut area is 3.75 inches except for the finest part of the nape area. I've been growing out the undercut for 9 months.
The top of my hair ranges mostly from 9.5 inches to 10 inches with a few areas with scraggly hairs up to 11 inches (25 months of growth) except for the very front widows peak area that is just a little past 8 inches. Therefore I can assume that the average growth rate on my head is somewhere between 4.5-5.5 inches a month.
The key to length retention for me is keeping my hair stretched with my revair and making sure that my hair is moisturized and sealed with Shea butter so that the shed hairs can slide out without taking others hairs along with it. This also helps me keep single strand knots at bay. I never allow my hair to shrink unless I'm washing it or doing a henna treatment. I alternate between low manipulation and protective styling mostly out of sheer laziness and 7 months of pregnancy. I haven't noticed a growth spurt from pregnancy and I haven't taken my prenatal vitamins consistently (skipping entire months smh and then followed by consistency for 5 days).
Overall I think it's important to measure your hair in tinier sections and at different seasonal periods to really gain an accurate understanding of your growth rate. Now that I know what my growth potential is for the year, I can set realistic expectations for growth goals without being disappointed in my own hair when I see someone else go from a twa to APL in a year.