Give me your map preselection algorithm and I will go through the map manually. Pressing F6 and visually analyzing map is boring and time consuming process. I was never that lucky as your algorithm according to the maps you provided. How many maps your preselection algorithm is reviewing in one second? It is impossible to accomplish the same manually. Bigger map will broke your preselection phase. You wouldn't be able to enumerate that many maps to find one without the obstacle on the way from start to finish in time.

Bigger map will also make much more difficult to decide where to go. The heuristic will be more difficult for a bot creator to code.

Also we should take into account that you are a bot owner and you aren't interested in arrangements against bots. You can try to foul the trail