A question to the OP.
Is budget a big constraint ?
I dont believe either Xcent or Amaze provide you any significant space capabilities over i20 other than a boot. Here too, its just 400 ltrs over 280 lt. Probably you should go for a C2 sedan instead of a compact one. Trust me, you will start feeling bored with these cars in just 1 year. Because they are virtually identical to your I20 in terms of interior space , ride and performance.
In fact, you should really see whether large boot space is a priority or not. If it is, then compact sedan is NOT the answer. You need to go to C2 where you get much more boot space, more interior space, better ride , handling and a more satisfying ownership experience. Only thing is, there are limited choices in AT. There are options like the Vento TSI, City CVT or even Verna AT.