As Fred says, you can't split the Right voice parts into three, but you can still set up three separate keyboard zones for voice parts by using the Left split and the Right3 split.
If you set the Left split higher than the Style, then the style will be controlled by notes up to the Style SP (when ACMP is on), but the left voice will now only play from the note above the Style SP up to the Left SP.
Now set the Right3 SP to a suitable note between the Left SP and the top of the keyboard and then Right1 & 2 (if turned on) will play from the note above the Left SP up to the note below the Right3 SP. The Right3 part will play from the Right3 SP up to the to of the keyboard.
As Fred suggested if you open the 'Split Point & Fingering' screen and turn on the style ACMP, all 3 right parts and the left part, the display will show you how the splits are placed, and you can see what happens if you turn off any of these parts.
I don't know if this will produce what you would ideally want, but it may be worth trying to get an idea of what can be achieved.
Regards
Ian