Answer

It is hard to determine something like that in a clear-cut way. In principle, a person can choose not to look, and ostensibly a woman should not have to behave differently so that he can look at her. By the way, Nadav Shnerb devoted an article to the parameters of modesty and argued that they are not defined by considerations of causing men to stumble, but on their own terms.
But human nature is such that it is indeed proper to take this into account, and it is hard not to look in the public domain. This of course also depends on the norms of dress in the public domain. A demand to deviate from the norm is not reasonable. The question, of course, is what the norm is (after all, today's secular norm also includes partial nudity). I think the parameters of "do not place a stumbling block" here depend somewhat on social norms.