Thanks very much for discuss about our API with us, that's very helpful for make our product get better.
I am really sorry I hadn't reply you so detail and maybe I hadn't think this problem more detail, and because I am also not the API designer so maybe my thinking is not without error. That's a good discussion here, I will let our development team knows it and they maybe can get more from our talking.
Here is my detail thinking about this problem:
1. Because our map is a control and most of our user is developer, so I think our API designer thought like a coder and default think our user have basic GIS tech. Here I have a question about your fist image, sorry I hadn't ask about that before, it looks you mark the right side about 200ft and the bottom side about 298ft, and the projection should be "+proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs", I want to know whether the 200ft and 298ft is screen distance or really distance. This just like GetDistance, I think for two points in GIS, if we need calculate a distance between two points, we need consider the projection information but cannot directly calculate the screen distance, just because for same two points, their distance looks different under different projection. So that's why if you want to get a standard buffered area, you need reprojection the shape, orelse it calculate the buffer based on 4326 and it won't looks correct just as you want.
2. For your technical item, because we implement that by NTS library, so we cannot convert the distance to lonlat before pass that into the library. About this I think our developer can do further research.
Any question about our product please feel free to let us know. Thanks for your detail post again.