could be the warm mod ua-5.
i'd say the same, my ua-5 is kinda bottom heavy. It was worse when i was using a shitty ol pioneer receiver, my onkyo cleaned it up quite a bit. But almost every tape i've made with the ua-5 has had a little more low end than i'd desire. I normally run rolloff to account for it. But different mic techniques also will help, XY smoothes the low end out with my rig and DIN is usually the best choice for me. good luck, hope you get some better results.