I will be referring to Christian Andersen's calculcations from https://forum.atlas-games.com/t/salt-mine-spell/9715/7
for base Aquam size. The +15 years update has been circulated to my collaborators and will be with you once figures have been checked.
By the way, does anyone have the size and might of the Remore of Virtue from RoP:M handy? I don't have a copy with me, and may want to use it when I get to having a familiar. (This is why I took Animal Ken - to justify communicating with and locating unlikely aquatic familiars without too much difficulty)