AC750 EX3700 Router light red but WiFi signal very strong

I want to improve the WiFi signal strength in my garage. Using Wifi Analyzer on my phone the signal is in the yellow. When I hookup the range extender where it has a solid green router light the WiFi signal in the garage vacillates between the top of the yellow range and the bottom half of the green range. If I move the range extender to the garage the router light on it is red but the WiFi signal strength is at maxium. Bandwidth is not an issue as the WiFi device is a garage door opener controller that doesn't need a lot of bandwidth.

So my question is which is a better setup in this scenario. Having the extender close to the router with a green router light but weaker signal strength or have the extender in the garage with a red router light but the WiFi signal strength at maximum?