You might know this already but for the benefit of Splinter owners who don't, the Splinter was never intended to be run in any mode but power. TCR mode doesn't actually control the temperature of the Splinter because it doesn't know the temperature of the Splinter. Instead, it's measuring the change in resistance and then applying an algorithm to vary the power in order to try to keep the temperature readout on your box mod close to whatever you've set. There are some variables in there that make this tricky, one of the biggest being the material the heater is made from. Another is the algorithm used, which is basically tweaked to make the temperature display look right, where "right" is what the designer thinks it should be. For example, the temperature displayed in TCR mode using @funkyjunky's tubo firmware is calibrated to a temperature probe placed at the load chamber of a tubo. Nobody has done the measurements for a Splinter.
I've been kindly informed that what I said here isn't entirely correct. The box mod does actually know the temperature of the Splinter heater by measuring its resistance. The rest of what I said still applies, however. An algorithm determines what is displayed, and it has to be tuned to the attached device. So 190°C on a tubo is not necessarily and most likely isn't exactly the same as 190°C on a Splinter.