We continue the discussion of "nominal" from the previous post with an example load-cell application. Sizing loads cells is easy provided that someone takes the time to do some simple trigonometry and engineering statics calculations. 1) "Best" is not the goal; 2) "Good enough" is the goal.
By good enough I mean that the load-cell system should be able to measure/resolve less than 5% of the lowest tension you ever expect to run. While wrapping more (or getting a better load cell) and getting to 1% of the lowest tension might seem like it is better, it will give you no better practical results. Thus, if the simpler Option A is good enough, then that is what you want.
However, if even Option B with the higher wrap angle is not good enough, you must re-iterate on the design. With lightweight webs, you may need to do more. You could, for example, use 180-degree wraps (pulling up) and lightweight carbon-fiber roller to get the tare weight down and thus get a smaller more sensitive load cell.
This is not only how we size load cells, but also how we size brakes, motors, cylinders, sensors and much, much more.