1. Right after Minato lands the Rasengan on Obito, the 4 Hokage placed a seal on Obito. This allows him to use FTG to instantly stab Obito, and he did.
2. Kakashi kamui a Naruto clone into the dimension and Naruto clone managed to hit Obito with a Rasengan.
So if Kishi wants, the current Edo Minato could teleport straight to Obito for a 1 hit. Or, Kakashi could assist Minato to kamui a kunai inside the dimension - effectively allowing Minato to use FTG inside the dimension.
In this way, Obito has no way to hide.