I think that the FT70 only supports half deviation mode and it can't be turned off, so you have to use C4FM Half Deviation modem mode on the OS2. In this case, please run C4FM Half Deviation AutoCal, or manually adjust the RX offset on the modem page for the lowest BER. You can listen back to your own voice using the OS2's built-in local echo service.
http://manuals.sharkrf.com/openspot2/en/control-calls.html#page-top