So if we go to the OData 4.0 specification: http://docs.oasis-open.org/odata/odata/v4.0/odata-v4.0-part2-url-conventions.html
I can't find any usage like InputParams(i_var='1'',''2'',''3'',''4'',''5') in the spec. My guess is that HANA XS is breaking the OData specification here, which is why PI can't parse it.
It's possible that XS isn't even supposed to allow this and the usage is an undocumented feature, as I can't find reference to it in the documentation.
Looks like the solution would be to use the REST adapter and craft the URL programmatically in PI.