[otrs] Problem with ticket numbering

Hi! First we decided that our ticket numbers should consist of 8 digits. Then we admitted that it is too long. I tried to change Ticket::NumberGenerator::MinCounterSize: to 5, for example, but OTRS ignores old tickets and creates new ticket every time customer response us in old tickets. I restarted the web-server and OTRS. The problem persists. Is this task possible? What should I do? -- With best regards, Ruslan