Offhand, I do not see anything that looks out of order with the dough formulation you are using. However, to get a better idea as to the crust thicknesses for the different pizza sizes, I calculated the thickness factors and got the following values:
12": 16/(3.14159 x 6 x 6) = 0.14147
14": 24/(3.14159 x 7 x 7) = 0.15591
16": 32/(3.14159 x 8 x 8) = 0.15916
18": 44/(3.14159 x 9 x 9) = 0.17291
I perhaps should have asked you what kind of pizza you are making, and what kind of carrier (e.g., screen or disk or pan) you are using, and what bake temperature and bake duration you are using, but the above values are much higher than I am accustomed to seeing here in the U.S. By the time you add sauce, cheese and toppings to your pizzas, they must really weigh a lot and take a long time to bake. I am not an oven expert but your oven may be a possible source of the problem you mentioned. To this, I would add that one of our Canadian members mentioned long ago that Canadian pizzas tend to be laden with toppings (see the thread at http://www.pizzamaking.com/forum/index.php/topic,7945.msg68235.html#msg68235
). So, maybe there is something you are doing in Canada that is common there but far less so in the U.S.
I also wondered whether 17-25 minutes of kneading at speed 2 of your Hobart planetary mixer might be too long and has produced an overkneaded dough that has adversely affected oven spring and the final crust texture. As you can see from Tom Lehmann's general dough preparation methodology as set forth in Reply 18 at http://www.pizzamaking.com/forum/index.php/topic,7499.msg64554/topicseen.html#msg64554
, the total mix/knead time is about 10-12 minutes. I don't see anything in your dough formulation that suggests that a longer mix/knead time is needed but perhaps there is something that I do not see from what you have reported thus far. For example, your hydration value might seem a bit low since you are using whole wheat flour in addition to your regular flour, but the amount of whole wheat flour is quite small and, in addition, the wetting effect of the oil raises the "effective" hydration to about 59%, which does not seem out of line, even if the Robin Hood flour you are using is a bread flour. Also, you already said that you tried raising the hydration value.
Maybe others will see something that I do not see, but the two areas discussed above--the oven and knead time--are what I see at this point as possible causes of the results you have described.