Sex with Insteads

I bought Instead Softcups because I heard you could have sex with them (I'm not a fan of using a towel underneath while having sex). I've tried but my husband says he hits it and can't get in. I think I put the cup in correctly (aim towards the anus, slide it in like a drawer, push the front in up to "hook" it). What am I doing wrong and how can we have sex with Instead cups?