I mounted my tach on top of the dash, because it was the most popular location back in the 60’s:
The story was having the tach mounted line of site would keep your eyes on the tach and the drag race starter at the same time. The reality is the main reason it was put on the dash was to show off that you had one.
Everyone else put there’s on the steering column, and I’ve had some mounted there as well:
Back in high school I mounted one in the upper left corner of the windshield just because I thought it looked cool.