i have a two-bike atera… can’t comment on the exact car tailgate combo you are talking about, or the difference between the 2 bike and 3 bike rack, but the version i have slides out of the way to allow the tailgate to open. have to do it when mountainbikes are racked, but obviously not when the road bikes are on there… 59 plate mondeo hatch, btw.
don’t know where you are considering buying from, but the folks at the roofbox co. have always been extremely helpful pre- and post- sales and can probably give you the heads up on the rack and the tailgate combo too.
cheers