hi Keith,
it is my understanding that the TA value of osmo-pcu is working as expected, as the timing offset is established durign TBF establishment. What osmo-pcu is missing is the PTCCH signalling to continuously adjust the timing advance as the timing offset evolves during an onging TBF.
So for a subscriber at a [relatively] fixed distance from the BTS (like the population centre you're describing), it *should* be working.
Please note that Sylvain has just very recently designed an open source "timing advance generator" under sysmocom contract, ant using that device (based on the PLUTO-SDR) plus some coaxial wiring/attenuators, it should be rather easy to simulate both static as well as changing timing advance.
The project is called 'osmo-rfds' (for RF Delay Simulator), see http://git.osmocom.org/osmo-rfds/
If OsmoPCU was just always operating at a static timing advance, I would agree that a VTY command would be a possible interim hack. But AFAIK, the PCU is not actually that limited ;)
Please help to clarify, thanks.