I think it's sometimes difficult for writers to know when to throttle back, especially when asked to talk about their projects. Seriously, just ask my girlfriend. If I'm working on a new story, the second she walks in the door I'll talk about it for 20 minutes nonstop.
But keep in mind, these publishers (especially the big ones) probably get hundreds of submissions a month. And they more than likely have to read through a lot of crappy proposals and boring ideas to find the gems. So I always feel by keeping your proposal simple and concise - leaving out ANY unnecessary details and frivolous language - and just focusing on getting the information across as plainly and painlessly as possible, it can only help you STAND OUT from the pack of other people writing mini-novels about their comics. I'm sure a well-written 2 page proposal (or 1 page, if you can pull it off) is just as good (if not better) than a 6 page proposal filled with clunky, boring sentences and superflousus details.
Instead of describing the plot page by page, perhaps it'd be better to go scene by scene, and even then, try and cut it down to one to two sentences a scene. Like: SUPERMAN IS IN A RESTAURANT WITH LOIS LANE. THEY ARE ARGUING BECAUSE HIS SUPERPOWERED FARTS KEEP KILLING HER PET CATS. UPSET, SHE LEAVES BEFORE THEIR SALADS ARE EVEN SERVED.
See, now if that were in a comic book, that scene could last for 3 or 4 pages.
Maybe you can post part of your proposal up and we can try and edit it down. Or don't. Whatever.