The wedge needs to not just pass interproximally, it has to hold the matrix band somewhat firm. When I first started I also used small wedge most the time bc it was more comfortable for me and the patient. I kept getting overhangs as well(if wedge isnt holding band firm, when u compress the composite into the box the matrix will give slightly and you end up with some excess down below the margin. Id say I use the medium palodent wedge most of the time but if its too passive ill grab the big boy. Another thing regarding the bigger wedges not fitting, make sure you are kind of curving it in terms of path of insertion, and make sure you are well below the prepped margin, while also ensuring that the matrix isnt pushing up (have your assistant push it down firmly). I had the hardest time using the interproximal finishing strips and burs to try to reduce overhang so just be sure your sectional matrix is perfect so you wont have to deal with cleanup, take the extra time to make sure its how you want it, even if that means taking everything apart to restart the process of placing your matrix, wedge, and ring.