Seriously bro, you might be diffusing and you might not be. my own diffusion drives me insane, sometimes I could swear its thinner on the top and sometimes not. I just shaved my head to guard 0 again(which I highly recommend for diffusers or people with decent hairlines but thin hair). TBH i really dont know about diffusion anymore. All I can say is, for 99.99% of cases its hard to tell unless its extremely obvious but then its too late. Just like most people said, go see a derm, the hairline is solid, but to check for diffusion map out your scalp. Using sensitive equipment they will be able to tell if your hair on top is miniaturizing in comparison to your side hair.