The smaller plant will have more transplant shock than the other but it should be fine. Regarding the sun, you cannot go wrong anywhere if shade starts at 11am or 12pm. That is what I aim for down here. Up in the northern states, it may be able to grow it in full sun in places where the sub is weaker. In the southernmost states, you need afternoon shade so the leaves will not get sunscorch. In KY, you are kind of in the middle so try and see with the understanding that right now, because the sun is still "weak", you cannot tell. So wait until the summer.
Plants in small pots have a little root system so hopefully it will recover. I am actually surprised that you could not find ES when you went shopping because I find it almost everywhere down here! Ha!
Feel free to move it at any time if you see that the leaves are turning all yellow -including the leaf veins- or yellowish, or an off white color. This will be more evident in the summer months. Now when the sun is not too harsh, you cannot tell if this 2pm location will work for sure. So in June-August, start checking the leaves often to see this happening. The affected leaves will be those in direct contact with sun. A single (or so) leaf yellowing out is just the plant doing its thing when it feels to drop old leaves and stuff like that. When you see a whole bunch of them yellowing out in the summer and all the leaves are in direct contact with the sun, that means it is not in a good location. You will not be the last person moving a hydrangea for sure!!! Ha!
Leaves that brown out from the edges inwards suggest that the plant is not getting enough moisture. You can cut these off and then try to keep the soil as evenly moist as you can. Nothing can be done about its lack of water when it got delivered so just prevent wet-dry cycles.
Red Sensation will also go through its own version of trasnplant shock but it may not be as severe. As long as you get a program established, it should do fine. In general terms,ysou can give newly planted hydrangeas about 1 gallon of water early in the mornings. Apply the water to the soil and never to the leaves as this can promote fungal diseases. If you get browned out leaves, cut them off. Hydrangeas tend to do some housekeeping in dry times and drop old leaves near the bottom sometimes but it should not be worrisome. I am talking about a few leaves only, of course.
Hydrangeas can become established in 1-3 years so not panic if this takes longer than expected.
* add a 1/4" to 1/2" layer of compost or composted manure in Spring as fertilizer for the whole year. Alternatives: cottonseed meal or a general purpose slow-release fertilize with a NPK Ratio of 10-10-10. During the growing season, feel free to sprinkle liquid seaweed, liquid fish or coffee ground but stop by the end of June so the plant will go dormant on time and not try to keep growing just as the cold weather cometh.
* At some point in the summer, you will need to increase the frequency of your waterings.
* maintain organic mulch levels of 3-4" up to the drip line
* water in the winter if the soil has not frozen and the winter is dry
* apply soil amendments to maintain the soil pH such that the leaves will not exhibit signs of iron chlorosis (the leaves turn light green to yellowish but the leaf veins remain dark green). This is common in alkaline soils.