Hi Si
Firstly I'm sorry to hear of your nerve problems related to diabetes. Your hba1c is very low, is this the cause of the retinopathy etc or has your a1c been much higher years ago?
Although I don't use the same set as you; I use a Tenderlink which is more or less similar I think. If you feel that the cannula is blocking with blood you can flush it with a syringe filled with some saline. The syringe needle will fit into the tiny membrane hole where the tube clip needle joins so that would free any blockages. It is fairly normal though for some blood to gather around the cannula hole. With the Tenderlink you can see where the cannula enters the skin as there is a small window in the infusion set. If this is what is bothering you, I wouldn't worry unless your blood glucose levels start to go up and you feel that insulin is not being delivered.