You are correct that setting Char_Pacing too long will defeat the purpose. The reason for adding an extra one or two stop bits is to prevent the problem where the SERIN software UART can misframe on a repetitive pattern and what it takes for the start bit may well be bit 3, 4, 5, etc. By giving the system 2 or 3 stop bits the SERIN command will fall into sync in just a couple of characters.

HTH
Brian