Well, on mine, which I just set a small speed square on, the answer is no, not exactly 90' from the rail surface. If you used a standard framing square (and I did) with the short arm on the top of the rail. the long arm touching the upper tie bar; there is about 1/4' space at the bottom where the corner meets the rail. It's very close to 90' but maybe 4-5' laid back towards the cowl. The best way would be to set it with the inner aprons at the top and the bottom would be the aforementioned 1/4" further towards the front. Hope that helps!