cooling off period after visiting for 6 months or less?

i assume this question has already been asked somewhere but i'm not sure if the answers are what i'm looking for so i decided to make my own topic.

last year in 2016 i visited the UK twice (from may to august// interval // september to november) and basically 'used up' about 4-5 months of my total of 6 months of being able to visit without a visa. i was wondering when the 'cooling off' period would start in my case (may, august, september or november?), and if i need to completely use up my 6 months in order for my cooling off period to start? this whole 'you can only stay for 6 months in a fiscal year' thing is a bit confusing to me as i've had an interval between visits and haven't stayed the full 6 months.

i'm also not entirely sure how long the cooling off periods are as i've heard its another 6 months or a full fiscal year, but then on this forum i read that it can only be 2 months as well for example. if my first visit was in may would the period start from there for 6-12 months or would it be from november when i last left?

i'm sorry if this question doesn't make much sense as i'm struggling a bit to word it. i'd be happy to elaborate on anything. if this helps with anything i'm a japanese citizen and studied illustration in london for 4 years (graduated in 2015). my visits were mainly for exhibiting at events and seeing people, in which case i wonder if i would be able to earn the long term visitor visa.

A Long-term visit visa only allows you to stay for six months per visit, just like regular visit visas. I assume you just mean granted entry as a visitor on arrival as Japan is a non-visa required country. I believe you must convince the border force officer your main purpose in the UK is temporary and you aren't spending more time in the UK than your home country (i.e. not actually residing in the UK) so a combined stay longer than six months per year would mean you clearly aren't residing in Japan but in the UK.