People would normally assume that Indian restaurants in an area with a high concentration of Indian restaurants are more likely to offer good food due to fierce competition and customers having plenty of other restaurants to choose from if a restaurant offers poor food or service.
However this does not always seem to be the case. I found a website which gives information about Indian restaurants in the curry mile in Manchester and the website includes reviews for some restaurants. Some restaurants received bad reviews. Have you eaten in a restaurant located somewhere with a large number of Indian restaurants competing against each other and you encountered poor food and bad service.