If you adjust them down further on the glass they'll look goofy because since they travel in an arc, they won't be level with the cowl/hood at rest, they'll be at an angle.
Can't lower the mount, because the mount point are the holes in the metal portion of the cowl, where the towers bolt in. Those are depressions stamped into the cab and I say it would take quite a bit of custom work to make them lower.
Finally, if you did succeed in making them lower that way, the chances they'll smack the cowl when running full speed, are pretty high.
If you hate wipers just remove them and Rain-X the crap out of your windshield on a regular basis. I drove a '61 Chevy for nearly a year with no wipers because the motor was burnt out and I was having a tough time finding the correct replacement. It rains quite a bit here. Rain-X is practically magic.
Richard