Before we hed in I apply it to each arm,(just in case I get a bad tech) about the size of a quarter but haven’t  run across that sort of problem with our techs here since he was a baby... before I had the cream they would be all over him looking for a good stick, even the tops of his feet near his ankle..  and tops of his hands... I guess I just hope for the best, luckily for him it’s been pretty effective, and his veins have been cooperative .. some veins  can be hidden pretty good .. as they get older and loose the baby fat in there arms it gets easier to see a good one.. find one that has worked or atleast been found pretty easily in the past and cream that one first...  I wish I could give you a better answer, .. It’s pretty frustrating to watch them fail and fail again all while your little one is screaming their head off.