That is incorrect, the wastegate does open fully (atleast with the BIC DDP). Infact the wastegate on the stock downpipe can only open up about 3/8", then the flapper arm hits the downpipe flange. I took this into consideration when I designed the BIC DDP, the flange is cut so there is enough clearence that the valve can open fully and opens up to 3/4". I also checked the Cooleeze downpipe and the arm also hits on that DP.
A bolt on Turbonetics turbo has a different housing style, but in the past had issues with the flapper binding in the housing itself.
The Titan DP is poorly designed with the first bend that comes off the turbo flange, the exhaust comes out of the turbo then hits the "wall" of the back of the dp, it isnt even a bend at the top, just an angled piecs of straight pipe. The BIC and other DP designs have a nice smooth bend at the inlet transition of the downpipe which is the best style for exhaust flow.
Randy@BIC