I know this is old, but for reference sake...

My redfoot knew about heights. for a while he was scared of black surfaces. We had a black coffee table and he wouldnt get off the paper towel without investigating it with his snout first.

In my experience, your tort should be ok as long as he can tell its a long drop down. And as long as he can see. We've had some mishaps almost happen when our tortoise was in reverse