Apple watch auto lock doesn't work

I have the apple watch sport and i am using it with Iphone 6.

I have setup the watch so that I can unlock it with my phone - phone unlocked = watch unlocked.

Problem is:

- Watch is locked

- i unlock my phone to do some random task

- watch unlocks

- i lock my phone however the watch doesn't auto lock

- i have to press the side button and select Lock Device - which is really annoying to do every time i use my phone

Does anyone know if there is an autolock timer I can set on the watch so that after say two min of inactivity to auto lock?