Ok, ussually the rank gap is every 5 matches from beginner-1stdan,and 12 matches from 1stdan-shihan.if you want it to reduce it, just go to tekken dojo then pick a beginner play one league match, then exit the tekken dojo then go to arcade pick the character(must be begginer) you used in the tekken dojo a while ago then you will rank in no time.
NOTE:when you enter the arcade dont quit or even lose one match or the glitch will end, the glitch can only be done once in every charcter(beginner)