It is true that the sea ice has a higher reflecting ability. It happens because ice and snow have higher albedo.
But at very high latitudes, where the sea ice covers the ocean there is a very poor insolation.
Thus the sea ice's higher reflecting ability doesn't cool significantly the Earth's surface.
On the other hand there is a physical phenomenon which has a strong influence in the cooling of Earth's surface. This phenomenon is the differences in emissivity.
The open sea waters have emissivity ε = 0,95.
The ice has emissivity ε = 0,97.
On the other hand, the snow has a much lower emissivity ε = 0,8.
And the sea ice is a snow covered sea ice with emissivity ε = 0,8.
Also we should have under consideration the physical phenomenon of the sea waters freezing-melting behavior.
Sea waters freeze at - 2,3 oC.
Sea ice melts at 0 oC.
The difference between the melting and the freezing temperatures creates a seasonal time delay in covering the arctic waters with ice sheets.
When formatting the sea ice gets thicker from the colder water's side.
When melting the sea ice gets thinner from the warmer atmosphere's side.
This time delay enhances the arctic waters IR emissivity and heat losses towards the space because of the open waters' higher emissivity ε = 0,95,
compared with the snow covered ice ε = 0,8.
Needs to be mentioned that Earth's surface emits IR radiation 24/7 all year around.
And the Arctic region insolation is very poor even in the summer.
That is why Arctic sea ice has a warming and not a cooling effect on the Global Energy Balance.
On the other hand it is the open Arctic sea waters that have the cooling effect on the Global Energy Balance.
Feedback refers to the modification of a process by changes resulting from the process itself. Positive feedbacks accelerate the process, while negative feedbacks slow it down.
The Arctic sea ice has a warming and not a cooling effect on the Global Energy Balance. It is a negative feedback.
The melting Arctic sea ice slows down the Global Warming trend. This process appears to be a negative feedback.