I consider switching to a soft suitcase. The size should be less than 158cm aggregately which I believe most airlines stipulate as the maximum size for free entrustment, but some soft suitcases, especially expensive ones like Samsonite, can usually be beyond the limit in a few cm or more.
This is especially true in suitcases that have redundant pockets on the front, which is openable without unlocking. They may also have expanders. And since the soft suitcase has more flexibility to pack into, the total size can expand more, depending on your contents. So the aggregated size can sometimes become 163 or even 168 or more, I think.
In these cases, do airlines care about these expanded size? Do they calculate the size of the baggage by the original size or by the actual, packed size?
Sorry if I failed to explain it well. The "original size" is not based on what a manufacture stipulates (which I just found written on the original post, sorry) but based on a straight line on the bag. This line would become a curve after the overloaded contents swell it up, which I meant as a "actual size". If the airline staff measures the baggage based on the edge of the baggage, it would be close to a perfect straight line and is considered an "original size".