Hello. Thank you for contacting the Toolset support.
Well - the thing is that the distance radius and radius unit (km,mi) is displayed using the placeholder %%DISTANCE%% as you can see with the following shortcode:
[wpv-control-distance default_unit="mi" compare_field="stud-city" distance_center_url_param="toolset_maps_distance_center" distance_radius_url_param="toolset_maps_distance_radius" distance_unit_url_param="toolset_maps_distance_unit" inputs_placeholder="Show results within %%DISTANCE%% of %%CENTER%% here you go"]
The only way I would suggest is using jQuery to remove unwanted distance unit option from the radius unit (km,mi) dropdown - sounds good?
You should try to add the following code to "Search and Pagination" sections Js box of your view to remove the km option.