I"ve got one of those oil wrenches that you sticka socket in as well. At first it started to slip the hexes. I found that it would grip better if i could stick the filter deeper onto the filter. I also found the restriction was because of the socket wrench sticking into the square hole at the top. So instead of sticking the socket wrench onto there first. What i do is i stick the oil wrench onto the oul filter first and i push it on as far as i need it to go. Then i take the socket wrench and stick it in as far as it will go. It may not "click" on like you had it before. But it does not need to. As long as the square tip goes into the hole you will be able to turn.

There you go... no more slipping...