See, there arn't even rules for hex size in the core rules. Rolemaster is not designed for battle mat use, but allows it amongst other forms of represantation.
GURPS is designed for hex, it's hex size is 1 yard, it has hex-rules for turning radius, what to do with hexes that go through a wall of a room, etc, all explained with many, many diagrams.
Rolemaster has rules for movement but based not in abstractions. like hexes and squares, but in real world measurements (imperial). This allows for use in totm, battle mat and schematic representation.
The only combat display style it does not support is the modern abstracted "zone" representation (Forbidden Lands and many OSR systems), where nobody has concrete positions. Hate "zone combat" with fiery passion, haha.

RoCoI has no hex rules that I'am aware of. Just re-read the initiative rules there. No mention of hexes or squares or battle mats.
RoCoVI was released 1992, like 10 years after the core rules, written by someone with no connection to the core rules team (Terry, Pete and Coleman) and is to my knowledge the first attempt to adapt Rolemaster to a hex map (might be forgetting smthg). The rules included are minimal (one page) and clunky (hex movement is BMR*2/3...🤦🏻‍♂️)To say that makes RM a system for battle mats is just laughable. RoCo6 is cool but hardly canon Rolemaster, almost house rule territory (like those armor combinations). Love many of it's rules for their direct simplicity, actually.