As knowledge of how STH status impacted postseason tickets in Cleveland...last decade as well as the 90s.
If you have full season tickets, you had first rights to purchase your individual season seats to all postseason games at a marked up price. Back in the 90s that was at a 250% markup on the tickets I know of for first round, and up to 400% for WS. Partial plan holders of 1/2 season had guarenteed tickets "near" their seats for 50% of the games, and in their seats for the other 50%. After that, it was all lottery. So lottery to partials first, then lottery to lesser partials, then lottery to full STH for extras, and finally lottery to non STH for whatever was like (probably like 42 tickets to each game).
You paid up front, and if you didn't want in on your seats, you got put in to the STH lottery to pick individual games. If they didn't play every game in the series or didn't advance, you applied the $$ to tickets the next season, no refund for STH tickets.
That's pretty much the way it is expected to work. Obviously there is a significant markup as these are limited and scarce tix in high demand. And it makes absolute sense that full STHs should have dibs on their seats for the playoffs. It would be unacceptable otherwise. If you own the whole season package for that seat, it should be your seat. Why should you have to give it up to somebody else? The reality is that if someone has only a partial package, they can't be guaranteed the same privelege simply because of the fact they are sharing that seat with others.
If there are two people with the same package vying for tix, it would make sense to use tenure as a factor in who gets a priority. But that is when all else is equal. If you compare a full STH to a partial STH, the priority goes to the former and they should absolutely have first dibs on their regular seats.
While I would certainly want someone who has been a partial plan owner for years to get some priority ahead of people who had just recently purchased packages, they can't expect to get preference over a full ST owner, period. That's not just because the full ST owner should have the rights to the seats they own, but also a simple matter of financial investment. The reality is that someone who has had say a 10 or even 20 game package for 13 dollar seats even since 2005 has only invested a fraction of what a full STH pays in one season.