Bain Capital figured it had some explaining to do after limited partners started asking why the Boston-based private equity firms holds on to 50% more in carried interest than other firms that participate in the same deals. According to The Deal, Bain wrote in a letter to potential investors in a new fund last month, that it partners with other firms as "an effective way to increase our pipeline of opportunities, improve competitive dynamics and reduce the risks associated with outside positions." As for why Bain takes a 30% carried interest while partners in so-called club deals get 20%, investors say that Bain puts in a lot more effort to clinch the big deals. The firm, according to a Web site document on partnering, says it usually takes a lead position in investments and pours in a lot of effort toward due diligence, and engages in aggressive bidding and follow up. In any case, the letter appears to have taken at least one limited partner aback. The partner told The Deal, "What is interesting to me is that Bain felt they had to address the issue at all. In whatever light they cast it, I am a bit surprised that Bain feels obliged to justify themselves, especially to a rather slavish investor base."