Tweaking the bed size is ignored

I have to print a full size part, for this purpose I try to tweak the bed size to a maximum. Unfortunately my TAZ 5 absolutely ignores “extended” geometry. The maximum amount I achieve is 275 mm Y-Wise. The bed has 300 mm and has still much freedom of movement and is not at its ends. The printer simply cuts the printout at 275 mm, there is no warning, no note anywhere. I checked Cura and Octoprint settings and entered 296 mm for instance, the slicer is showing the print path also beyond the 275 mm but the printer simply ignores it. I assume it is fixed somewhere in the firmware? Any chance to change this?

Side note: the X-Axis is a bit longer than the Y-Axis, so I can fit when rotated, however still wondering about the restrictive behaviour and where it comes from.

Thanks for any hint

We store the bed size/axis travel range in the firmware as well: (note, this is for the TAZ 5 with 0.50 mm hot end nozzle)

// Travel limits after homing
#define X_MAX_POS 298
#define X_MIN_POS 0
#define Y_MAX_POS 275
#define Y_MIN_POS 0
#define Z_MAX_POS 250
#define Z_MIN_POS 0


You can change these values by downloading the firmware source files, changing as needed, compiling, and ultimately flashing your custom firmware to your printer: