Maybe this useful for other Users too...
I don't know the exact English wording in Tasker, as my Version of tasker is German, but i think you should manage to follow the steps..
i managed to get auto reconnect working on the nexus 5 using Tasker:
1. new Profile: Status --> BT Connected --> Search Name of paired Gear Fit --> Search Address of Gear Fit --> nothing on "inverted"
2. new entry-Task: Name it "BT reconnect"
3. select Network Bluetooth --> select turn off and then go back
4. select "+" at the bottom menu to add another step to your "BT reconnect" task
5. select Network Bluetooth --> select turn ON again and then go back
6. Go back to the profile-page and long-tap on the green arrow
7. Change the Activation from ENTRY to EXIT, so you should have a red arrow instead of the green one before
if you set all this up correctly, then every time the Gear Fit goes out of bluetooth range, Tasker turns your Bluetooth on the nexus automatically OFF an back on again.
On my Nexus the Bluetooth OFF/ON procedure is enough to get the two devices automatically reconnected as soon as the gear fit is back within bluetooth range of the nexus 5. Tested several times today in normal allday-situations and worked perfectly.
Maybe this helps also the HTC One's...