Bench Legs: Angle and Placement Questions

The questions are:
"What angle should I use for the legs?" and "How far in from the ends of th e seat should the leg assemblies be placed?"
The following is a prototype of the bench I'm building. The dimensions are set and the real pieces are already cut. I'm sure that some will have opini ons as to the dimensions of the bench itself, but we're not going backwards. We're going to have to work with what I have.
Note: The prototype only has 1 leg assembly and a short stretcher. The bloc k of wood at the far end will obviously be a matching leg assembly.
https://i.imgur.com/CghUIAj.jpg
The bench will be 60" long, 14" wide, 18" high, no back. The prototype was built to the same width and height.
The seat is 1-1/2" thick. The legs are 2-1/2" square. The stretcher and other miscellaneous supports and braces are 1-1/2" thick and cut to aesthetically pleasing widths.
As shown, the legs are cut at ~12.5° and placed so that the bottom of the legs are 13" wide. (1/2" in from the edges of the seat)
Question 1: Is 12.5° a good angle? I like the look, I just want to be sure that it will be stable enough.
Question 2: How far in from the ends of the seat should the leg assemblies be? I'm thinking that centered on 9" in from the end of the 60" bench might work. Obviously, once I decide on the angle and build them, I can pla y around a bit, but I thought I'd toss the question out anyway.
If the 1-1/2" poplar seat has any sag in the center, I can always add upper stretchers. I'm already planning on 2 diagonal braces from the leg assembli es to the bottom of the seat. (not shown)
Thanks!
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