Funny but on the other side what type of lighting are you using on the smaller tank ? Different lights , different spectrum , different intensity, and with a shorter tank it would be different par . He moved for a reason . For health reasons I would make sure all the other water parameters were good as well as lowering the intensity of the light and bringing it up slowly to acclimate. You didn’t mention if you had rock or someplace for it to hide from direct light if that is the issue . Anemones tend to move where they feel comfortable whether it’s current , light , or even where they feel they are better set up to snag a meal . If you want a anemone in your tank to stay in place where you put it , they do sell nice plastic, rubbery ones at Walmart’s lol!, . Sorry I just had to throw that in !!! . Good luck