I've always used grids. Currently, for HARP, I play totally metric to teach my children to think in metric. So each 25mm grid square is one meter. And we use 54mm figures 'cause we have a gadrillion 54mm plastic soldiers (Roman, Viking, Medieval) and its actually to scale with the grid map. Anyway, we play "loosely". In other words, distances are all approximate and positioning is always most favorable for best flavor and common sense. Movement is always approximate. So we just guess at distances and do what "looks" good.
But if you like exactitude - I would use the grid NOT to position the figures - let the figures be anywhere. Just use the grid to make quick measurements and help with drawing. Use a ruler or templates for measuring and movement. Dowel rods or wood skewers with 1" marks (to represent meters, 5 feet, whatever scale you like) work great. Longer measures can be done with a tape measure. That's the way table top wargaming is done.
In my opinion, facing (flank, rear, etc) should be obvious given the position of the models and always giving the defender "best" choice of facing if the defender is aware of all attackers - ie turn for free. In other words, if a character is aware of a lone attacker, there is no way the attacker should get a positional bonus if the defender can turn normally. Sure, first round surprise - you get position - but otherwise no.
This does NOT apply to characters on horseback, really large lumbering creatures, characters charging or otherwise running, characters maneuvering heavy loads or polearms, stuck in the mud, et cetera. Characters and monsters in such circumstances don't get to turn freely and so would need to make a maneuver roll and the attacker might even be able to maintain flanking position by moving every round (at penalty to attack of course).