Narrow gap groove

The steep flank weld has a small opening angle. This means you need less filler material and introduce less heat into the part. That's good for thick material because it reduces the risk of hot cracking. But be careful that the flank doesn't become too steep. If you can't get in cleanly with the electrode or torch, the weld remains incomplete. Then you get lack of fusion or cracks in the weld belly. So: set it steep, but always so you can still hit and fill the root cleanly.