...How?
The Jackson already has horrible amounts of over-penetration for all of Ost T3 and most OKW vehicles.
Buffing the long range pen will hurt heavy tanks more, sure. But when you're never bouncing on a PzIV or StuG anyway, it's going to made nada difference to the PzIV/Jackson combat outcome.
When you only bounce 1 in 100 shots to begin with (never mind if you pop your special super rounds), the functional increase in average damage per shot is utterly trivial against medium tanks.
It's like saying that buffing Jagdtiger pen would hurt the t-70, it's not going to even begin to matter...
OK, let me say it this way: buffing its pen without reducing damage will make it more viable vs heavier armor, sure, but it won't change the fact that OST T3 is useless, T4 is overpriced and OST will still have to rely on heavy call-ins.
Horrible amounts of over-penetration only applies to the StuG and Ostwind, the PZIV has 180 armor but it doesn't really matter.
Every stock TD (SU-85, JPIV) has good penetration but 160 damage. Why does the Jackson have to be the exception? Good penetration (after proposed buffs), 240 damage and a turret.
I totally support a pen buff, but at the cost of damage otherwise it would simply be too strong.