Guido - be careful what you wish for here. If you have a short stubby mast that you can look over, the top of the mast will have cross braces that will become in line of sight as you lift. So rather than looking through a window of a clear view mast, an unnecessary obstruction will come into view with a short mast that could be even worse.

Have you thought about a telehandler? This removes the mast altogether and JCB who launched impressed on the forward visibility advantage. There was also a Swedish Company who made a machine with the mast behind the cab but both this and the telehandler, whilst increasing forward visibility, will bring lateral (left and right) visibility shadows!