FBA storage limit and inventory performance index


Hello Everyone,
If my IPI is lower than 350 all the quarters and they give me storage limit, does the limit change or does it stay the same if it stays at 350. I have now 2200 Cubic space in FBA, i will never pass the 400IPI, i am wondering if the next quarters it will stay at 2200 or it will keep on lowering… Thanks alot.