I am not sure why you would think production at PEP11 wouldn't...

I am not sure why you would think production at PEP11 wouldn't lower NSW gas prices. The main problem NSW faces is that it imports 95% of it's gas, predominantly from Queensland these days. This is expensive. There are three potential alternative supplies, PKIT, Narrabri, and PEP11.

PKIT - not viable under the current price cap as it would be importing gas from WA, Twiggy won't advance a zero margin business.
Narrabri - huge pipeline infrastructure yet to be built but likely to be cheaper than PKIT.
PEP11 - closest to the market of the 3, will onshore adjacent to existing pipeline infrastructure.

But, here's the kicker, in reference to your comparison to the WA reservation policy, the proponent of PEP11 has publicly committed 100% of PEP11 gas to the domestic market. Santos haven't made that commitment for Narrabri and the giveaway will be if the Hunter gas pipeline connects to Wallumbilla.

Any NSW end user seeking a GSA will not be able to source gas cheaper than from PEP11 due to the lower cost of transport alone.