I suggest top or middle, not the bottom. If placing beads on bottom close to the Oasis, might absorb 100% RH all the time and not be able to absorb more if needed. I place mine in the middle to absorb extra the Oasis might give off, but have them on the top sometimes. Really the Oasis is the main RH producing source and the beads are there to absorb the extra or give a small buffer (at least here during the summer).
Winter air here is dry with the forced heat etc., so the Oasis works more often than during the summer and the wine cooler gets un plugged. As less air is circulated in winter, I place the beads up top.