9688 vs 3593a, Fram makes a distinction in these two filters that other manufacturers do not. The 9688 being mostly for Hyun/Kia and there is a slightly different bypass spec. Most others like Wix just combine the two applications in one filter, in this case 51334.
As for looking for a larger 'non' OE spec filter for 'more media area' and 'greater oil capacity'. Jim Allen stated after speaking with engineers that, "the average filter in the average car at the average OCI/FCI is less than 50% loaded when removed." And when it comes to using a larger filter to increase overall oil capacity, whatever increase it likely insignificant to total oil capacity. Also, highly unlikely to have any effect on engine wear and/or longevity.
In this case the mention of vehicle warranty is very important, imo. Kia with that lifetime (or whatever) warranty, should something happen while using a non spec OF, there would be no filter warranty coverage. Not only that, but I suspect that if Kia found a non spec OF on the vehicle, they too would NOT cover any engine warranty in the event of a failure.
Lastly, the 51334/(Fram 9688) and spec equivalents plenty big enough for the Kia 1.6L, all day, every day.
