The latter, if it fits at the top. The drawer side panels are blocked by the shelf under the oven, about 5mm. It cannot go higher because then it wouldn't fit at the top again. According to Ikea, it should work...
Where is the space supposed to come from then? It might only work with Förvara. If you look at
and
it looks like the upper edge of the frame is slightly lower in FÖRVARA than in Maximera.
I can't say that it fits well and comfortably, but it works. The drawer front does not close perfectly flush with the carcass, but you can fit everything in with a lot of tinkering. Not necessarily recommended. I will ask at Ikea again.