As you might have gathered from the above, the scale of the miniatures matters.
3" hexes or larger are too big for most single-engine 1/285 and 1/300 planes – they look lost and spaced too far apart. For 1/285 fighters I found 2" hexes were about right. I played an entire Korean War air campaign on 2" hex mats and never had a problem. Most single-engine planes fit without overflowing the hexes, or only overflowing a little bit. However, stepping back to WWII, most twin-engine bombers in micro scale are more than 3" wide, so they overflow a 2" hex quite badly, making formations of them quite a problem. The four-engine planes are even worse, typically exceeding 4" between wingtips. The full CY6 30x45 hex grid fits within a 9'x5' table with 2" hexes, which is really convenient.
My CY6 roup plays on 3" hexes with 1/144 fighters, 1/200 medium bombers, and sometimes 1/300 or 1/285 for the really big planes (heavy bombers, giant flying boats, etc.). I recently started my own collection of 1/200 AIM fighters (cheaper, more durable, really fun to paint) and they look great in the 3" hexes, plus they are in scale with the 1/200 medium bombers and less out of scale next to 1/300 heavy bombers.
A 3" hex mat for CY6 is a bit of a problem. For a long time my group used three 6'x4' Hotz mats, but that way the grid is only 24x45, so the long edges are often 3 or more hexes too close – only sometimes a problem, but a PITA on occasion. Late last year several of us ordered custom 30x45 hex mats with 3" hex grids from Deep Cut Studio, and they are gorgeous and durable, but huge and costly (€165 shipped). The full 30x45 grid is about 7'-8" wide and 11'-6" long, so it needs a BIG table to fit. We're very committed to 3" hexes and play a lot, so I have no regrets, but it's a lot of cash to blow if the game might be a flash-in-the-pan with your gaming group.
FWIW, my group also uses telescoping rods to demonstrate altitude, which makes it a bit easier to fit oversized planes in formation – we can always adjust each rod just a bit up or down so the wings overlap without touching. If you're playing the usual way with all planes at the same height, wingtips overflowing hex sides are a much bigger problem.
- Ix