1/2 inch is OK.
I agree. Before the first flight, I shortened my RV-8 front stick to allow my thumb to be on top of the stick and pass under the panel bottom. It turns out that the front stick in an RV-8 is shorter than one would like, especially when flaring to land. In 500 hours of flying my 8 it has never been necessary to push the stick under the panel with my thumb on top. After 400 hours of flying, I welded tubing back on to the top of my stick to lengthen it to about 1/2 to 3/8 inch below the panel base. This stick length is better than it used to be and seems to work fine.
Dan Miller
RV-8 545 hours