Yes, this is normal. Thicker blood, it is darker and thus it is farther away than lighter blood. I learned this information from a friend who studied to be a fletobomist at these courses https://phlebotomynearyou.com. He tells me many things that I didn't know before. He is fast-paced and I believe that he will be a good specialist who will be able to help people. I remember how he told me that in practice one guy lost consciousness when they took his blood for tests. This is a big risk, because you don't know how a person will behave in different situations.