If you don't know what I'm talking about, it's the tendency to attach
Suvalkija up to the Nemunas River to an independent Poland, often in the form of a panhandle, in AH maps and timelines. If you are not picturing it in your mind yet, here is a visual representation of what I am talking about:
I hate hate hate hate
hate hate hate it anytime when I see this happen. It irritates me as much as successful Sealion threads irritate British members, or as much as French surrender monkey jokes irritate French members.
Why? Because Polish Suvalkija is impossible without the intricate circumstances which happened in OTL to make it happen (for a grand total of 20 or so years, maybe a bit more).
You see... Before the end of the 18th century (and, in almost all ways, also afterwards) Suvalkija was a land integral to Lithuania as much as Samogitia or Aukštaitija. Much like Samogitia once used to be inhabited by a Baltic tribe which assimilated into the Lithuanians, the same happened in Suvalkija (which is where the alternative name for the region, Sudovia, comes from). It was only in 1795 that the region was split from the rest of it's ethnic territory - in the Partitions of the Commonwealth, of course.
We like to joke about the arbitrary borders made by the colonizers in Africa, but really, the borders set by the Partitions were almost as bad. Entirely new borders were drawn, splitting ethnicities in the Commonwealth between the partitioners at their whim - and this exact thing happened in Lithuania, too. For one reason or another, Prussia and Russia decided that the border between them should go along the Nemunas, and this way, they created the abomination. Fast forward 10 years, and in 1807, after the Treaty of Tilsit, Napoleon threw a bone to the Poles and reorganized the territory Prussia got in the Second and Third Partitions into the Duchy of Warsaw, almost accidentally giving this Polish state parts of Lithuania in the process. So while the arbitrary nature of the Partitions separated Suvalkija from Lithuania, Napoleon's successes in his wars resulted in it being attached to Poland, setting up the cliche.
It didn't matter much at the time, of course, because as the Poles hoped, Napoleon will soon hand them the rest of the territories they lost in the Partitions, including the rest of Lithuania, but, surprise, that didn't end up happening, and a slightly smaller Congress Poland - but still with Suvalkija up to the Nemunas - became an autonomous part of Russia instead. This kingdom lasted a mere 16 years before being incorporated into Russia... and that's it! Poland never specifically laid claims on Suvalkija ever again - in fact, the parts of Suvalkija which belong to Lithuania in OTL are perhaps the most Lithuanian parts of the country, and were also the source of the Lithuanian National Revival. During World War I, Suvalkija became a part of the established Republic of Lithuania, staying with it until today.
So, after this long diatribe, what do I have to say about this?
1) Having Suvalkija be owned by an independent Poland is only possible with a very specific set of circumstances (the Partitions of the Commonwealth happen as in OTL, the Duchy of Warsaw is still founded like in OTL, which basically removes any major pre-Napoleonic POD);
2) The possibility of a Polish Suvalkija border is only possible in the first half of the 19th century, and even then, it is almost certainly not going to be long-lasting - either Poland retakes Lithuania, or geopolitical and strategic pressures will force them to abandon Suvalkija one way or another;
3) If you want to have Poland own Suvalkija regardless, even having them hold it as far as into the 20th century, or even the 21st (god forbid!), then trust me, I will find you and I will force you to write about how Poland deals with a large, densely packed and angry Lithuanian minority in the north and how it impacts their relations with whoever holds the rest of Lithuania.