I think you are right that it is too warm. I have 10 ducklings that will be two weeks old tomorrow. The ten of them are in a 6-7 foot indoor pen. They have access to their old, little brooder which has a heat lamp at only one end and is where their food is. They also have a four foot baby pool with brick steps to get in and out. Mine have been spending most of the day on the end of the pen farthest from the heat lamp, sleeping (where the bucket is in the video). They get up after about a half an hour and go swimming, get some food, or run around. I tell you all this to say they really do not need a lot heat at this age. They also do really well if they have room to move around. It sounds like you are doing a good job and figuring it out. Your duckling are going to enjoy when that pool arrives!We do unplug the heat lamp during the day and at night we plug it back in because it gets colder. Currently I have them on all flock food because we have chickens as well so we can feed them both the same food. I have them on vitimans that have quite a bit of stuff including niacin in it, and I’m giving them hydro hen in their water as well. I personally think it could just get way to warm in the sun porch during the day.
These are mine last week: