well, that's your problem.  you can't fit an inferno window of that
size into rio (you have to take into account the 4-or-so pixel rio
border too).

you'd have the same problem if you tried to use the window(1) command
to create a new rio window of that size.

try -g1000x760 (which has the additional benefit of leaving you a
little "plan 9 space" around the edges...

  rog.