Cover letter : how to value one's experience at Elite Boutique to go to BB Bank without saying too much how great it is

Hi,

I am currently applying for summer internship in BB Banks and I've performed a 6 month m&A internship at an Elite boutique.
Of course, I gained a lot of experience and the fact of working within a small team gave me a great insight and lots of responsibilities, and i guess , more than i would have had i had worked 6 months ( as a Junior level) at a BB bank.
I am currently doing my cover letter, and I would be very grateful if you could give me some clues on how i could value this experience at an EB, without saying too much that EB are great since we have more responsibilities etc ( i don't want to sound like I'd better go again to EB since the learning experience at the junior level is that good)

Thanks a lot,