Sorry WillLem! My English is not as good as I would like and looks like I didn't use the idiom in appropriate context. 
What I meant was:
That particular tweak you suggested(1entry per designer) was based on good intention(encourage people to participate in contests) but would possibly end up getting something not good to what is more important.(reduced opportunity of level designing)
Though awarding 3rd place is not hard to do(if we decide to do so, the mixed round with 3levels becomes the final and that's it) and an easy way to let more designers get appearance in the high rounds.
Always letting 3 different designers to progress into the final round needs more refined and extra rules, and probably more works to do for the contest organizers, but still something we could try.

What I meant was:
That particular tweak you suggested(1entry per designer) was based on good intention(encourage people to participate in contests) but would possibly end up getting something not good to what is more important.(reduced opportunity of level designing)
Though awarding 3rd place is not hard to do(if we decide to do so, the mixed round with 3levels becomes the final and that's it) and an easy way to let more designers get appearance in the high rounds.
Always letting 3 different designers to progress into the final round needs more refined and extra rules, and probably more works to do for the contest organizers, but still something we could try.