The true difference between the attribute of Gevura versus Chesed-Gevura is an overflow of Divine energy and not contracted energy:[1]

Gevura is one of the attributes of God. Thus, unlike the common misconception that people have that this attribute involves contractions and abstinence from giving G-dliness[2], in truth it is in increase and overflow of G-dly influx and revelation, and comes from the wording of Tagburos, which means “strong flow.” Accordingly, the flow of energy from the infinite light of God is more from the attribute of Gevura than it is from the attribute of Chesed. It is due to this reason that also below by creations, not all creations are able to receive from this divine light as it is too high and intense, and there is a judgment that takes place prior to a creation receiving from it to see if he is befitting of this life. This is in contrast to the attribute of Chesed which is cool and calm energy and therefore is able to be diffused below to all creations without distinction. This then is the true meaning behind the statement that God initially desired to create the world with the attribute of judgment, and after saying that the world would not endure it He decided to create it with the attribute of kindness. God originally wanted to create the world with the tremendous influx of godliness that is diffused from the attribute of Gevura, however, after seeing that it was not possible for all the creations to receive from it, He decided to create the world from the more calm and limited attribute of kindness. In this respect, Gevura refers to the world of Tohu in which the seven premortal kings resided, and while originally God desired to create the world from Tohu, He instead created from Tikkun which is Chesed based. [A parable to understand the above can be taken from a stream of water which enters into a cup from a faucet. There are two ways in which water will not enter into the cup; either due to not opening the faucet or opening it only slightly so only a few drops fall in, or through opening it to the highest pressure and having all the water enter the cup and bounce right out. In order for the water to remain in the cup the faucet must be opened to an extent that water will flow, but not with too much force. The water not entering the cup is compared to the attribute of Gevura, while the water entering the cup is compared to the attribute of Chesed. Now, people usually understand the attribute of Gevura to mean that there is a very contracted level of G-dliness which is diffused, which is comparable to only very little water entering into the cup. The novelty of the above statement of Admur is that in truth the attribute of Gevura contains much more forceful diffusion of G-dliness then does the attribute of Chesed, which is compared to a very high pressure faucet which bounces the water off the cup.]

[1] Torah Or Noach p. 9c

[2] Vetzaruch Iyun, as Admur himself in numerous places including Shaar Hayichud Vihaemuna, explicitly explains like what he defines here is a misconception, that the attribute of Gevura conceals and blocks the G-dliness.