How to make a spherical ramp based on distance


Hi all,
I’m new to Maya but not to 3D and looking for a solution to a problem i can’t solve. I tried to project two different HDR panorama on a single mesh. I succeeded with a mix material and doing a mask for the blending. Now i’m looking to automate the mask step : i’d like to project a spherical gradient from the same coordinates than the place3Dtexture node that drives the panoramic projection. The problem is that there is no ramp style based on distance. I’ve seen this post that looks interesting : Distance Based Ramp?, but i can’t make it work. Any solution or advice will be very appreciated