When we were TTC, DH didnt withdraw straight away but waited a few minutes.
The month we conceived, was the first time we had DTD and not had any "spillage". I got him to be on top that time and not withdraw for a few minutes afterwards, and then put a pillow under my bum to elevate that area, and I didnt get up for a little bit.

I always found that if I was on top, as soon as I moved all the spermies would come out, so I always aassumed that was unhelpful if TTC.