Taste of spelt vs. white whole wheat?

After a 5-year hiatus, I've recently begun baking again, and I've been trying out the method and breads in Ken Forkish's FWSY. One revelation is that I can make bread by hand-mixing, so I don't need to haul the heavy mixer up from the basement!

One recipe is Harvest Bread with Poolish, in which I increased the whole wheat content (using KA White Whole Wheat flour) from 10% to 20%, which I find quite agreeable.  Then I noticed BRM whole spelt flour at the market, so I tried a loaf using that in place of the WWWF and was a bit disappointed to find that it seemed to taste no different.  So I baked another loaf of each so I could compare them directly, with the same result.  A few blind tests with other subjects produced the same results.

From what I've read, spelt seems to be admired for its mild, nutty taste, and I'm comparing it with white WWF, which is also milder than regular (red wheat) WWF, so it this to be expected?  Or is 20% not enough whole grain to yield much of a taste difference?