Is there an optimal height or is it more a case of personal preference so long as it doesn't cause any issues?
The received wisdom seems to be that the tailpiece should be as low as possible, but without the strings touching the bridge behind the saddles (which is usually only a problem with the E strings, anyway, because of the way the saddle height is staggered to match the fretboard radius)
But yes, it is personal preference. Some people like the "top wrapping" approach where you feed the strings through the front of the tailpiece then wrap them over the top - this gives a very shallow string angle behind the bridge which, as you've seen, reduces the string tension a bit.
The problem doesn't usually arise on guitars with a vintage Gibson ABR-1 style bridge, because the bridge is so narrow. But most manufacturers use the wider Nashville style bridge.
The neck angle and even the trussrod adjustment come into play as well, because if the bridge itself is low to the body, then the tailpiece can sit low without the strings touching the back edge of the bridge.