Generally hot and fast yields less char, but some materials char more readily than others (cork, mahogany, zebrawood, etc. all char extensively).
1/4" material puts you on the back foot already, because it’s naturally going to need more laser energy to cut that much material. Have you tried doing a full power 2 (or more) pass cut test?
The benefit would be that you could go faster at full power, and the two passes would potentially yield a less charred outcome.