Passing parameters with email redirector

So I'm doing some email testing passing users off to different surveys with a redirector:

My example redirector is here:

https://optisightsps.tt.omtrdc.net/m2/optisightsps/ubox/page?mbox=redirector_1&mboxDefault=https://boehringeringelheim.eu.qualtrics.com/jfe/form/SV_6GtxALf4vwYWKuV?testParam=test

This will go via Target and hit the below redirect offer:

and the user will finish here (as per the re-direct in Target):

https://boehringeringelheim.eu.qualtrics.com/jfe/form/SV_6GtxALf4vwYWKuV?L1=star&L2=placeholder1&Q_PopulateResponse={%22QID2%22:%221%22}&mboxSession=111586910737299-301552

Notice my ?testParam=test was not passed onto the final destination URL (Above) even when I have the include URL parameters checked in Target, I have also tried my redirector in the below format but still no luck:

https://optisightsps.tt.omtrdc.net/m2/optisightsps/ubox/page?mbox=redirector_1&testParam=test&mboxDefault=https://boehringeringelheim.eu.qualtrics.com/jfe/form/SV_6GtxALf4vwYWKuV

What I want to know is if passing a URL parameter is possible with an email redirector, and if so how. If this is not possible can anyone think of another solution for achieving this?  

If this is not possible then it should 100% be a feature request as it makes redirectors pointless.

Thanks

Dan