Even though the post is so old, I'd like to highlight that even without assist nudging Filia forward it is still possible to fake crossup using j.mk. This just requires the opponent to be standing at full height. In fact I'd like expand on this.
If you could get the opponent to be standing still on the ground, cross ups become very tricky with Beowulf. You can fake a cross up with j.lk or j.mk depending on how early you press the button. The earlier you press it, the more likely you will not cross up. You can test this yourself by just doing press slam for a good horizontal space between you and your opponent. And try pressing j.lk or j.mk at different times during your jump. I've tested on peacock where I could press j.lk very late in order to get the crossup where most of the time I wouldn't have. It wasn't press slam space though.
Now I don't really know how useful this is. But it seemed interesting to me.