How to calculate using geodesic distance when working with GeometryEngine.CreatePointAlong() ?

[KevinCheriyan]

I'm using the .NET Maps SDK and GeometryEngine to calculate x distance (in miles) traversed along a polyline and drop a point there. I'm using the CreatePointAlong() method to achieve this. However, when I run this, I get a resulting point that is measured using planar miles. I want this distance to be measured using geodetic miles. How can I achieve this? 

My polyline that's being used for the calculation is in Web Mercator (WKID:3857) which is a projected coordinate system with units in meters. Could this be the reason for why the distance measurement is planar?

Here's the WkText for my polyline's SpatialReference: 

"PROJCS["WGS_1984_Web_Mercator_Auxiliary_Sphere",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Mercator_Auxiliary_Sphere"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",0.0],PARAMETER["Standard_Parallel_1",0.0],PARAMETER["Auxiliary_Sphere_Type",0.0],UNIT["Meter",1.0]]"

What else have I tried?

I tried reprojecting the polyline to NAD83 using SpatialReference.Create(4269), but this changed the unit of the polyline to degrees. I need to use miles in my distance measurement, so I believe this is useless.

And finally, I know the resulting point is calculated using planar and not geodetic distance because I compared with ArcGIS Pro's Measure tool which lets me measure using planar and geodetic methods.

Any help would be appreciated! Thanks!