Suppose each congregation in a presbytery were no more than one hour from every other church in the presbytery. (This principle could apply in other polities, too, even among congregational polities.) This would be small enough that all the ministers and elder cadres could have steady, organic relations with one another. This is closer to the way presbyteries used to be organized. In some places, especially in the west, this rule might not be practical. Still, I think a one-hour dispersion rule would be a good rule of thumb for the Presbyterian Church.
I am working on a document about rebuilding the Presbyterian establishment. In the draft, I argued that the Executive or General Presbyters, the ongoing staff person of the presbytery, is a natural advisor to the General Assembly. The EP, though, is not a constitutional officer. The constitutional officers -- the offices every presbytery has to have someone fill -- are the stated clerk and the moderator. I also believe the stated clerks are natural advisors to the General Assembly. The moderator usually serves for only a year, so does not have quite the breadth of experience that the stated clerks and EPs have.
A reader of my presbyterian establishment draft commented that EPs are a recent invention. In order to assure that most presbyteries had the resources to afford a permanent paid staff member, the presbyteries were made much larger. In much of the country presbyteries today far exceed the one-hour rule.
If going to one-hour presbyteries meant doing without EPs in most places, so be it. I think it is more important to the life, connection, and solidarity of the church that the local ministers and elder cadres know one another.