I have been using the avent breast shields from the day i started BF, recommended by my gerfren. I like it cuz like what you said it 'catches' the leaking milk whilst baby is nursing on the other side. but i dont face the 'overflow/leak' problem you are facing. you are referring to the leaked milk contained in the shields leaked out whilst adjusting? Did you see if the soft rubber is properly encasing the hard shield?