No, it fit without any modification. I have not tried it at the range yet. I love the finger plate, much better than the one that came with the TH9C. I also ordered the 17 round from them as well and ordered a sleeve for it on ebay.
Another option for the "Pinky" is to replace the magazine base with one from Galloway Precision (www.gallowayprecision.com).
For $12.50 you can get a base that supports your pinky finger AND adds another round to the magazine, making it a 14+1 instead of 13+1.