Well, I like to a get a bit creative with my model placement, treating them a bit like a mini-diorama (As much as 6mm models allow). Some models are clustered together in the centre of the base, back to back, others may be strung out in a loose skirmish line on patrol for e.g. Using the edge of the base allows for consistent measurements and modelling freedom and is generally pretty standard in most wargames (so it's not harder to draw LOS, coherency, engagement range, templates with some of my stands of models than others). It also accounts for the abstract nature of the game. My stands take up the area of the base but at this particular freeze frame in time are in these positions within that area - as they interact with the enemy and move around the battlefield they won't stay in those positions.
An example being:
Models are not evenly spaced on all bases, so the easiest and fairest thing to do is to use the base itself for measuring. Sometimes this means they can extend their engagement range a tiny bit but it also means that they are harder to hide and can be brought into the opponent's range a tiny bit. The important thing is that it's consistent.
