Wow, that takes me back. Those instruction no longer apply, let me explain. One of the innovations that Zifer (AutoHome) made was to integrate the roof tent's deck with the bars so the bars were and integral part of the tent. Before that all the tents like Hannibals and the lot used expedition baskets for support which were heavier than the roof tents. This allowed AutoHome's tents to migrate to small cars and the tents weren't just for expedition vehicles anymore. The instructions you have are for use with the old steel expedition ladders. The ladders were two parts, the lower part would sink into the dirt when you stepped on it stabilizing it and the upper part was supported by the tent's side. All your weight was supported by the edge of the tent and could twist and develop stress cracks with time because of the flexing. Having the crossbars go out to the edge supported the edge. The newer fiberglass is better too, pretty much anything you find in North America is the new stuff, much better than "marine quality", hence the reason why your Maggiolina's shell is a good 20 pounds lighter than the new tents that look like AutoHome tents.
So, if you have an old steel two part ladder, keep it as an antique or have it for expedition use and order one of the new alloy ladders. Bottom line, don't worry, your tent can handle the shorter bars now as long as you don't use the steel ladder.
An aside, if you read the instructions, you will notice that these tents were designed with only one door, the other side was a small triangular window. Maggiolinas were really well adapted for cold weather use. Even though you could specify another door on the other side, the ladder wasn't designed to go there, it would interfere with the lift mechanism. The new Maggiolinas have a different lift mechanism so the ladder can go on either side. The old lift mechanism was bomb proof, in fact, even though the tents were and are very high tech, they are designed to be repaired in developing countries. The old steel ladders were often used as sand ladders and would get all twisted, no problem they still worked and you could weld on them if you needed. The new alloy ladders aren't welded, they are assembled to be able to be able to take them apart to repair. Probably costs twice as much to assemble but they have kept to their expedition roots.