I've read that the A7 can be bottom fed.
A-7's are my current "go to" for bottom fed devices. They do of course require some modding... Like most, I drilled air holes in the covers, stabilized the center pins, and sealed the bases with 10mmX12mm Buna-N O-rings. They are the best "low budget"
rba's I've found so far for bottom feeders, but they don't compare to Igo's vapor output, taste, TH, etc...