Drainage mats and foam – GreenBuildingAdvisor

Question for those familiar with using Drainage Mats along with exterior foam: is it necessary??

Working with my local building inspectors on this wall design and they are not familiar with any foam thicker than an inch.

My wall assembly (central MN zone 6):

drywall with class iii vapor retarder

2×6 wall with at least r-19 batts

1/2” osb

tyvek commercial housewrap

2 layers 1” xps

1 layer 1/2” xps taped seams

3/4” furring strips

possibly another budget housewrap

Ascend siding

My inspectors finally agreed that I could do this much foam (initially they were telling me I couldn’t because of fastener length concerns – see here for that thread and more details: https://www.greenbuildingadvisor.com/question/minnesota-code-requirements-with-cei   ) but want me to add a layer of “Drainage Mat” on top of the Tyvek and before the foam.

I have no doubt that it would not hurt anything, but seems to me unnecessary if I’m already including a rain screen outside of the foam and will add another $2k to this wall assembly.

Are there requirements in the code book for this?  They keep telling me their requirements and when I ask for where in the code they are referring I get no response until I find something and then they say, okay we’re good with that!  

They are generally pretty good to work with and have been open, but just are clearly not comfortable with exterior foam…