I'm currently running Conjure animals quite restrictive
The player says that he is casting the spell and designates the places where they will appear (then I label them, as they are designated). I roll which animals take the form of a table that was designed to fit the whole Bell.
However, this has now bitten me in the butt several times, since the animals evoked campaign table often do not fit rubber and road encounter. I've got War Horses on sloping and slippery houses, vultures in dark, damp basements, and a rhinoceros in a narrow hallway.
While this was often humorous, I wonder if I should re-roll animals that clearly do not fit the meeting place. Are fairy spirits summoned "smart" enough to take a form that fits the place of invocation?