The decision to thermal at 500ft AGL is the same at the finish sector, out on course or attempting to thermal out from a relight near the airport. It's irrelevant where this is taking place. If this is affecting finishing gliders, I suggest to move the finish up to 1000ft so that if there is really someone who is trying to thermal up at 500ft AGL, that there is enough separation that he does not affect the incoming traffic.

If you want a hard-deck 4 miles out to prevent pilots from electing bad judgement and thermalling low near the airport, then why is it okay to do so 5 miles from the finish? Or 50 miles from the finish to not land-out? I don't necessarily support the hard-deck nor am I opposed to it, but if you follow this sort of logic presented, that's a great reason to have a harddeck completely around the whole task area. The decision to thermal at 500ft is still the same decision, no matter where the pilot is.

Best Regards,
Daniel Sazhin