I just realized I forgot to emote the kidding tone in the first part of my statement, ahh! Apologies if I came off too strong!
It's your project, so define it as you will. I just wanted to have a little more interesting of a solution than just hiding them behind the leading edge. Excelsior was a prototype in many ways, so if I'm writing my own guesses on it, might as well make that an interesting new take on the tech that never caught on, either.
I figured that blue top was the same construct as whatever flanks the Refit Enterprise warp nacelles. One plan calls this structure a Thermal regulator system, so I guess it makes sense. Excelsior is using a bigger version of a technology introduced in the 2270 refit a little over a decade prior. Whatever this is eventually morphs into the surround system used in Ambassador/Galaxy successive designs, probably replacing the bussard collector system I described above.