I had my sixline in a few different open topped tanks, he never jumped.
I would be leery about the other wrasse though. Might be OK at first but it's hard to say what will happen over time. My sixline was a model citizen for many years but after a few years he did become a holy terror towards a few more docile fish I had (tore the fins completely off a mandarin I had, who ended up dieing from his injuries
)
Can you put some gutter guard over the overflow so that he can't be chased into it? Or double up the eggcrate (and offset) so he can't fit through?