Non salaried income combined with tax declared tips

Hi,
I hope I'm not asking a previously asked and answered question but if so I apologise.
I am my fiance's sponsor. From the beginning of July 2015 until the end of December 2015 I earned £6786 in my waitressing job. I received £3780 in tips. My company takes no responsibility for tips and does not operate a TRONC system. I declared this money to HMRC and received a letter in August stating that they are now deducting tax for that through my pay from the restaurant. I have banked that money, either once or twice monthly.
My questions are;
What does this money count as? It's not cash in hand pay or self employment or through a Tronc system. What route can I use to apply for our fiancé visa?

Can we apply after 6 months even though this money is not on any payslip?

Thank you for any help you can offer,

N

It will probably be classed same as overtime pay as it isn't a definite salaried payment.

If you have no proof of the 'tips', HO is likely to question this money and bank deposits. HO will expect to see a paper trail of where the money originated.