I would not like to try it, but has anyone tried a 2" adapter into a 1 1/4" receiver in order to accommodate a bigger rack?
Not sure if this is the correct answer to your question but the Thule racks, have a 2" end that goes into the hitch. There is a metal sleeve (for lack of a better description) that comes off and vola` you have a 1 1/4. Is that kinda what you were asking?
Looking at that rack, the instructions state that it should only be used on Class 2 receivers. I assume that the only issue of Class 1 v. Class 2 is the total weight (tongue weight) of the two different types of hitches.
Shoredad, is that the "stock" mazda rack? On the Mazda site the rack looks much higher then yours. I haven't gotten a roof rack yet and yours looks good.