Hosted Polygon Geofence for Survey123

[WilliamRockwell1]

So I've read some articles on how to restrict a survey submissions via geography. One works with min/max coordinates and another mysterious method alludes to using reverse geocoding. The first isn't particularly useful for odd shaped polygons, and the other isn't actually articulated.

For example: If I have a river channel polygon that has a snake-like shape, a big rectangle around the entire polygon isn't going to keep out the points that aren't in the river channel.

I would like to be able to designate a hosted feature layer and have Survey123 only allow submissions within that layer. (pretty please)

[RobertBorchert]

Could you make a feature layer polygon around the stream and have that be the selection to start the survey and it creates the point at the location the survey is taking place

[WilliamRockwell1]

Possibly, but the survey isn't always being completed on-site. 

[WilliamRockwell1]

The ArcGIS Solution for Citizen Problem Reporting does this when configuring the web application. I was hoping Survey could do the same.