I've never heard that. It should take the same kind of SIMMs that other Macs of its generation take, so you should be able to get any size up to 128 megs.
If you're looking on eBay, the way to be 100% certain it'll work is to buy one that says it's for a Cobalt Raq2. You can ignore the EDO part - the Mac will ignore it, too - but the SIMMs for the Cobalt will definitely work and they'll definitely not be too big (the Cobalt is a 1U, after all).