Try this as a finishing move, not throughout your entire bicep routine for each move. For example, a drag curl or dumbell curl for 3 sets, then a hammer type move for 3 sets, then a finishing type of move for 3 sets.
For me, having my arms outstretched to either side (performing almost a double bicep pose) and hitting them at their peaks (like you say.. only about to 1/4 from the bottom,1/4 way to top) seems to hit the muscle at the peak of it's highest point.