Over the last few years, I have been writing several papers in the same direction as part of a research program. This means that the same exact setup is introduced at the beginning of each of my papers: i.e. the basic assumptions on the categories I am using, the basic terminology and notions, etc. As you can imagine, there are only so many ways of stating the same exact assumptions over and over again in each paper and now the first one and half pages of all my papers are beginning to look very much alike. I am a little worried: is this some kind of misconduct? Even though the content of my papers is different, is this "self plagiarism" or something when the first part of the first section looks almost identical to that in other papers? 

I should mention here that by "first part of the paper", I am not talking about the introduction. Obviously, each paper has different motivations and different results and hence different introductions. I am talking about the first page of the body of the paper, where you put in stuff like "Let C be a category satisfying ....yada yada yada...and we will denote this operad  by this and so on..."