Right now, the ranged potency soul augment Pettas Soul, compared to its melee and technique counterparts Daityl Soul and Nex Soul, are very hard to obtain due to the limited options available to farm them.
As it stands right now, both Daityl Soul and Nex Soul can be reliably farmed in the field to an extent. For the former, Daityls commonly appear at the end of PSE bursts in combat areas and have a veteran spawn location in South Aelio. For the latter, Nex Aelio has a chance to appear in Resol Forest and can also be farmed from the Nex Vera UQ.
For Pettas Soul, according to sources I've read it's supposed to be able to drop from level 15 Pettax mobs, but is extremely rare and I personally have maybe only seen this happen once in the first three weeks of NGS' lifespan. The only other place to get it in a more guaranteed environment is the Pettas Vera UQ, which is all but guaranteed to drop one I or II capsule. However, this means in hindsight that it's only possible to obtain one Pettas Soul capsule every 4-6 hours, depending on how often UQs pop.
The end result is that obtaining Pettas Soul is heavily gated compared to Daityl and Nex Soul; Where as the other two can be reliably obtained from the open field, Pettas Soul is not and almost relies solely on an urgent quest. For people using ranger or gunner and/or use rifles, launchers and TMGs, this is not very fair.
On ship 2, this disparity can also be seen in the personal shop at this time of this post:
Daityl Soul: 2k (I) / 31k (II)
Nex Soul: 2k (I) / 38k (II)
Pettas Soul: 7k (I) / 68k (II)
So my suggestion would be: Assuming that lv15 pettax enemies do actually drop it, to increase the drop rate of Pettas Soul on pettax enemies to bring it more in line with how much Daityl and Nex Soul drops in the field. As pettax are more common this would mean the drop rate would still have to be kept low, but enough that ranged weapon users aren't waiting 4-6 hours to get 1 capsule for one of the better ranged potency focused soul augments.