Printable area of Deltas (Rostock, 3DR,...)

Hello,

I have checked that my 3DR has it's virtual limit in the square circumscribed in the circular platform. Visual explanation:

That is, I'm able to move the extruder to any point in the 260mm circular area but when I try to print something (sliced in Slic3r) it stops at the virtual squared limit of 183mm (green area in the picture).
Is it possible to turn the whole circular area into the printable area (green + red area in the picture)? I guess it's a stupid error setting up the firmware (Marlin) or a parameter inside Slic3r because manually the extruder goes to any point...

Any idea?
Thanks