The doctors are correct in that it is best placed on fatty tissue, I also use sure t's and have them to be the best infusion set for me but I only use my tum, however as your son is a baby and you're talking about having to increase his correction doses then I would suggest you go back to your doctor and get him to check the sites and see if there's any issues with the sites there. They are best placed for checking for lumps and to ensure the sites are all ok to use, sure t's are the most effective infusion set for accuracy based on my experience of using other sets which were plastic cannula sets, so I can't see how the infusion set would be the issue, it sounds more likely that the sites may be the problem.