Hot Flex applies at 160C.

If you are only getting the temperatures you are saying then it looks like the press is not working properly. Try wacking it up to 200C to see what temperatures you get.
Some cheaper presses don't hold heat between presses, and in some cases the heating element only kicks in when the press is open. So if you are printing a longer run of garments the temperature drops of considerably simply because there is not enough time for it to return to the correct temperature.