If you run out of elevator authourity then it's not that the CG is too far ahead but that you need more elevator travel. Use dual rates or exponential for the high speed portion if needed.

If the real one blanketed out the elevator then yours will too. I don't recall any such worry with the real one though. Also we often say this or that was blanketed and that's why this or that won't work. But the number of true cases of being blanketed are few and far between. More typically there is something else at play such as incorrect CG locations or too much or too little elevator travel. The bottom line is that if the tail volume is very low there's two things that are needed to make the design work. First is to move the CG ahead. Second is to use a symetrical or lifting airfoil that has a very low pitching moment. You chose the Clark Y for your U2. It may well be that the relatively strong negative pitching moment of this airfoil combined with using flaps is why you're losing elevator authourity. If this is the case then moving the CG ahead will help but not by as much as it would if you had used a symetrical section or a flying wing airfoil with a very low pitching moment.