tapering the outside or the inside of the PTFE tube is asking for problems. And let me explain why real quick. While you are thinking this will create slack and allow the filament to move more freely what you are actually doing is allowing the filament to come out of alignment with the precise hole it is supposed to line up with at the very end of that ptfe tube. Personally I like to use Capricorn tubing as it has a smaller id and will even more precisely locate that filament as it transitions from the ptfe to the heatbreak.

One big question I have about your conversion is did you calibrate? That is did you first set the temp sensor calibration in your firmware to what the slice engineering thermistor is? And then second did you PID autotune that heater? Because Slice engineering likes to use 50 watt heater cartridges that are a bit different than the 40 watt we see everywhere else or the high precision 30 watt cartridges that E3D uses. If you have not PID autotuned your heater then it can swing over and under target and create all manner of problems and if you did not set the right sensor calibration you are not running at your commanded temp.