A sampling assembly of a single packer assembly may have more guard drains than sampling drains. The single packer assembly having the sampling assembly may be deployed in a wellbore formed in a subterranean formation, and the single packer assembly may be deployed on a wireline cable or another deployment or conveyance. The number and the area of the sampling drains, the number and the area of the guard drains, and the positions of the sampling drains and the guard drains may be designed so that the guard drains which are operational may provide a fluid intake rate exceeding a predetermined threshold if one of the guard drains is congested and/or blocked.