I had this problem constantly with my McMillan A5 - it would always break the seal on my Howard Leights, so I did double ear pro. I just got a KRG Whiskey 3 and the cheek piece doesn't extend back as far on my face, and it's just smaller than the A5 cheek piece. I took it out last week for a few rounds and had zero issues with my Howard Leights breaking seal like I do with the McMillan. Not sure what rifle you're using, but try taking a look at a KRG W3/XRAY and getting behind one if you can. It might fix your problem.
Regardless, you should definitely double ear pro it. I used just ear plugs on a stage at the last match I did, and the ear plug started work loose in the middle of a stage, and I had to readjust it. Sucks, because there were a crap ton of hard stages for a beginner like me, and this was one of the easier ones, but I lost a lot of points due to the ear plugs coming loose. Tinnitus is not your friend. Protect them ears.