MR1100 - External AP used via ethernet - slow connection

I have a MR1100 which works fine on WiFi connection with speeds up to 90mbps, the issue I have the signal range. To expand the range I have connected via ethernet cable to an existing Access Point router to spread the signal further which works however I only get around 10mbps. Can anyone tell me what is restricting the full signal from being passed through the ethernet connection + AP and also how to resolve this?