Those two spells are actually very different. IIRC, Earth in a Pot shoots random bullets while Galaxy in Pot aims them at you, making it notably easier. In both cases, starting out very low on the screen will make some familiars go off the bottom and vanish. Further, in Galaxy in Pot, if you destroy some familiars and them stream towards/away from the gap in the circle. no bullets will be aimed at you from that spot (which is to say, along the same line as your movement), making the streaming much easier. Against Earth in a Pot, if you destroy a few familiars near the top, take their place in the ring, and then follow it along as it expands, you'll have to deal with far fewer bullets, and they will all be coming from (basically) one direction rather than all around you.
That's what I remember doing anyway. Reimu and Yukari can't really take the familiar destroying approach as well as the Magic and Ghost teams.