I agree - more like a blockade. MacDonald complained about his troops being left in five garrisons and asked permission to abandon the town as the troops were need in his corps:

"It is worth noting that if the total number of troops under the Duke of Tarente was at that time, nearly 17,000 men, he could hardly have had, in fact, 9,000 to 10,000 men at most for active operations. The remaining troops were blockaded, and formed the garrisons of Grave, Wesel, Venlo, Jülich and Maastricht. [6]
...
[6] Macdonald had made a correct account of the dangers of the situation. In the dispatch he sent from Kleve to the Chief of Staff on 1 January, he asked to withdraw without leaving people in the fortresses. But in responding to him by letter dated 10 January and his note of the 12th of the situation in France, the Emperor could not bring himself to sacrifice and give up the towns of countries he conquered.

"Macdonald to the Chief of Staff. --Kleve, 1 January."

"...The enemy defile without interruption towards Gorinchem and Breda. Rest assured, Monseigneur, that in a few hours or a few days, they will have broken into Belgium. The Allies maneuver their wings and demonstrate before us at the center. Gatherings at Düsseldorf, Mühlheim, Deutz and at the mouth of the Sieg have no other purpose than to wait for this irruption to intercept the routes of Coblenz and Luxembourg, while that of the Campine (Kempen) the enemy blocks the path from Brussels and Namur."

"I repeat to Your Highness that troops so spread out have no strength, that taken obliquely and head on, this huge line will be a distraction, useless for the general defense. The towns themselves will not help. The complement of supply is still too far to serve. The 5th Corps and 11th, assuming they can throw themselves into the towns without being cut to pieces, only amount to 8,000 to 10,000 men, including the bayonets of Wesel, two or three more at Grave, Venlo, Maastricht, Jülich. For the five towns, it takes more than twice this, and in any case, it would only leave a little more than an army corps on campaign."

"We are touching a great crisis: would it not also be wise to carefully weight a high resolution? That taken, under such circumstances, the places so remote; lacking in part; weak garrison; which will soon succumb and without benefit to the State ... In the current crisis, at the moment where the old France is being pierced, would it not be wise to abandon the new by rallying all the scattered detachments, the growing of conscripts in march and men with national honor and French blood that will come under the eagle of the Emperor ..."

"What is the use of maintaining for the Emperor this isolated corner of the Empire, when the barriers of the Rhine and Meuse are crossed. I will not hide what all French murmur; they only want to defend their country, that he cannot find here, or succumb with honor under the ruins of France!"

A few days later in a dispatch in which he sent on 7 January, to Maison, he added to the translation of a proclamation of Blücher: "Blücher doesn't hide the plans of the Allies and we remain isolated, scattered. By being thrown into towns poorly armed, poorly supplied, those that are we needed so much to defend our homeland, we bury it in ruins!" (Archives of the War.)
... " From Greg's excellent translation of Weil:
http://www.napoleon-series.org/military/battles/1814/Weil/c_Weil4a.html

"16. Die Festung Jülich.

Sie wurde von dem feindlichen General St. Loup