Perhaps some designs use more smaller warp coils and other designs use less but larger warp coils. Discovery has thin nacelles verses the Enterprise. Likewise the Sovereign has thinner nacelles next to a Galaxy. Defiant has a few large warp coils for its combat frame, but a Nova has longer nacelles.
The nacelles of the pre-2151 Intrepid-type Earth starships were considerably bigger and bulkier than those of the newer, bigger and more advanced NX-class of starships. But those vessels were still smaller, slower, less heavily armed and generally less effective in combat situations or traveling at warp than Enterprise or any of the other ships in her class.
Klingon Warp Wings FTW, they give you so many design options in terms of Warp Field Emitter placement that can't be done with normal Parallel Warp Nacelles. And there are 8x Different Type of Warp Field Emitters that I've catalogued so far within Trek. So there is ALOT of diversity in terms of how you generate that Warp Field along with the PRO(s)/CON(s) to each method of doing the same thing.
So the basic takeaway is that you can't go by the nacelles in determining how fast and powerful a ship is.
It was a rather long-winded way of just saying warp nacelles generate warp fields, and depending on the ship design, some are more streamlined in shape than others. Basic Warp Geometry 101.
This is all conjectural, theoretical hypothetical physics anyway. So there might be some precedent for different lengths and coil designs in nacelles to affect speed, efficiency and perhaps even the lifespan of the hardware itself. Take a design like the Sovereign Class. After the events of Wolf 359 and the re-emergence of the Romulans after close to 100 years, the possibility of war must have become far more visible to Starfleet in general. It would therefore have made sense to build a ship with long Nacelles with particular coil design and hardware with the intent of a rapid response ship. Given that we don't actually have a canon maximum speed for the Sovie though, it's impossible to prove in Canon. This is in high contrast to the Galaxy Class and her Nacelles are most likely designed for long cruises to the edges of Federation Space and back. Built to be very reliable and versatile to keep itself on the move as much as possible for various diplomatic and first contact missions taking place anywhere in Federation space. Another example is the Intrepid Class. Though probably designed and built several years after the Galaxy, it too incorporates a shorter and more robust nacelle design. As a science ship it makes sense to have another ship capable of long cruises to survey systems and various anomalies on the outskirts of federation territory and even into uncharted space. This and it's new technological advancements such as variable geometry warp nacelles and bio-neural gel packs were also to benefit this mission profile and co-incidentally helped the USS Voyager in it's journey back to the alpha quadrant. The new nacelle design seen on the Sagan and Connie III at least by their 'look' and proportions could be to find the perfect balance of high speed and long-term efficiency.
I'm sure most people here will have seen EC Henry's video on warp coils: His TL;DR here seems to be that the total volume of warp coil material seems to be important and much more comparable that the shape of the nacelles – long skinny nacelles and short fat nacelles would ultimately have similar volumes of warp coil material, and ships like Defiant or Voyager, which have unusually small nacelles, have extremely dense configurations of coils. I have a headcanon idea which broadly aligns with this, which is that different shipyards had different design principles with different sets of trade-offs. What we might call the "Utopia Planitia" design school became very dominant in the mid-24th century, with fat rounded shapes and elliptical saucers, starting with ships like the Ambassador, the New Orleans, and the Springfield, and culminating in the Nebula- and Galaxy-classes. The "San Francisco" design school favoured lean, long, skinny designs, starting with the Constitution and the Excelsior and culminating in the Sovereign-class. A good way of directly comparing these design schools is to imagine that, separation abilities aside, the Prometheus and the Intrepid are essentially the same ship, but designed according to the SF and UP schools respectively. The SF school favours increasing ship volumes by primarily adding length above all else while keeping everything streamlined and structural, while the UP school favours increasing volume by making the ships stockier, wider, and much more rounded.
I kinda like this theory. Plus, it's kinda supported by what we saw of Utopia Planitia in "Relitivity." Just viewing the episode, I could really only make out mostly Galaxy and Akira class ships under construction, plus one Excelsior, that could have just been in for repairs.
Anyone remember when that early teaser came out all the gnashing of teeth and cries of ruined childhoods across the internet?
The unprecedented brown hull colour is still weird, but the shorter nacelles and lack of negative space in the saucer are definite improvements.