If his fluid is watery more then thick it will. Also if he pulls out some and doesn't deposit as far back as he can. I have to lay down for 40 mins after. Then it will come out still after about 3 hours or so. It is gravity but the sperm should swim up and it just be the slow swimmers
and fluid come out after the 40 mins. Oh yeah my RE told me 40 min. You also need to make sure you have a pillow under your butt. It is not just his fluid but yours and if yours is watery then it can wash it out faster. Not a problem though so don't worry but lay there longer and everything will be fine:)