ISRO's announcement Announcement of Opportunity (AO) for future Mars Orbiter Mission (MOM-2) says in part:
It is now planned to have the next orbiter mission around Mars for a future launch opportunity. Proposals are solicited from interested scientists within India for experiments onboard an orbiter mission around Mars (MOM-2), to address relevant scientific problems and topics.
This “Announcement of Opportunity (AO)” is addressed to all institutions in India currently involved in planetary exploration studies / the development of science instruments for space. This orbiter mission will facilitate scientific community to address the open science problems. The Principal Investigator of the proposal should be (i) able to provide necessary details of the instrument which can address the scientific problems and (ii) capable to bring together the instrument team and lead the team for developing a space qualified instrument.
The payload capability of the proposed satellite is likely to be 100kg and 100W. However final values are to be tuned based on the final configuration. The apoarion of the orbit is expected to be around 5000 km. (emphasis added)
I can udnerstand that things like the estimated mass (~100 kg) can be specified as they are highly dependent on the launch vehicle's capability. Stating the power estimate of ~100 W suggests to me that the spacecraft's bus will be managed by ISRO and they are budgeting roughly 100 W to support the experimental payload.
However I can't venture a guess why the apoarion (apoapsis of the Mars orbit) has been chosen to be around 5,000 km, and why a lower, circular orbit has been excluded for at least part of the mission.
Question: Why would ISRO's MOM-2 Mars orbiter mission's apoarion already be decided in such an early call for proposals?