Hi, having only flown Cessnas and Pipers, I have not seen the mixture check mentioned in any published checklist, but it does seem to be a reasonable check, if you can understand the principles involved.
One thing I would like to ask, is, would you do an A check if just taxying from hangars to parking?
The reason I ask is that the only plane that I ever got loads of water out of the fuel was a club C152 (which was on loan.) which had been run the half mile from the Hangars onto the Dispersal-Parking area by another pilot.