Slide brush gives edge, please help -->

The block right under the block that is supposed to be the surf/slide gives edge. Meaning I can stand on the block and not fall down. How can I fix it? I know it's fixable, but how? I've tried func_illusinary, but then it becomes unrealistic because the bullets goes right through it.

Here is the screenshot with more specific explanation:
http://i46.tinypic.com/2uo01aq.png

yep like nerv. said you need it made as one block, since cliphull adding extra surfaces around brushes, so you can stand there coz you get extra surface from the block beneath you