Mine does it using the regular default standard letter settings, I didnt make any changes to anything.

Suggest you look at ProSeries users guide, chapter 18. Hope that helps. BTW as Lisa said mine works fine, made no changes

So my standard recipient letter shows this for the partner info, not sure why yours is missing and you need to add it, but maybe this will help?  Not sure if the formatting will come through, I might need to give you a screen shot.

<@PTRNAME>
[@PTRADR1]<@PTRADR1>
[@PTRADR2]<@PTRADR2>
[@PTRADR3]<@PTRADR3>