My workplace subscribes to a startup mentality and our seating is made up of long double-sided tables that are each five "desk" pieces locked together end-to-end. Anyone is free to sit where they like and move chairs around as desired. As an introvert and someone used to a lot of elbow room, I find putting five people on each side perfectly reasonable as there's nearly enough room to spread your arms out and not touch your neighbor doing the same.

However, many of my coworkers will scoot multiple chairs into one "desk" area, often spilling over into my section. I will shamefully admit to attempting to mitigate this by both staking claim on an end to at least free up one side, as well as getting in early and moving any extra chairs on my side back where they belong (and possibly pushing my neighbor's chair to dead center of their section and out of mine before they get in).

This works well enough in a preventative manner, but sometimes I get in later and someone's already settled halfway over into my section, or someone will come over to consult with my neighbor, pull up a chair, and suddenly be halfway into my space.

As much as I recognize how silly this is on the surface, I find having someone sitting that close insanely distracting. I'd like to say something to ask if they wouldn't mind moving down a foot or so but I don't want to come across as rude or antisocial. I'm asking here first because I don't even know if this is reasonable to ask for, or if I should just suck it up and deal.

My workplace is fairly casual and I do joke around with my coworkers a lot, but almost everyone is my senior in both age and experience. I do not share a boss with any of them and on top of that our hierarchy isn't one where I'd want to bring this up to an authority figure. I'd rather just hash it out with them.

Clarification from the comments:

• The person sitting next to me could be any of a number of coworkers and vary from "I see them daily" to "internationally-based coworker who comes in once every 6 months for a company event". My level of acquaintance with them similarly varies from "very friendly" to "polite nod in the hallway". I'm looking for a polite way to request more elbow room that would work for any of these scenarios.
• There's enough room for everyone to take a desk (there's two of these long tables, plus conference rooms if people need to group up). Others are just more social than I and/or seemingly need less elbow room and would prefer to clump up, or will come over for a question and then not go back to their original seat for ages.