This is an old script that needs to be updated for polygon collision to get your collision up to expectations.
The old method used parameters called 'hull' and 'fat/narrow' which only supports collision within a defined bounding box that is usually set by the orientation of the model, e.g, a rectangular shape like the tank form would have good detection one way but bad when rotated away from its orientation at load up.
read later editions of AUM to find the solution you want.
Cheers.