Salary Negotiation

So I have been in talks with a German bank to join them as a senior analyst. The applicationasked for desired salary per anum, which I filled in, but halfway through the selection process everyone told me the city I was going to was the most expensive in Germany, and scaring me about housing prices this and that, so I decided to ask them for more. I know it is not very professional to change my expectations half way through, but I prefered that than regreting it afterwards. I also asked about the bonus, I knew it is not fixed, but for a range, to better estimate total comp. They told me is ranges from 0-200% of the fixed but normally it is 10%. So with that I gave them my expected salary per year.
The issue comes when I received the offer they gave me what I asked annual gross, but that includes a variable part (10%), and I thought I was negoting just the base and on top of that I would have a bonus.
Just for future opportunities, how do you think it is the correct way yo do it when they ask for compensation expectations, talk just about the anual base gross? I find it pointless to negotiate the bonus as a number when in the end they can do whatever they want with it.