Hi,
The reason I suggested smaller prey was that it kept the same feeding schedule so was less disruption to the snakes eating pattern.
He won't notice if the rat is 45g instead of 55g but he will notice if it is 3 days late.
As to the space issue I would use a smaller water bowl and throw the log away - the hides are more important than the log and if the humid hide fixes the humidity issue then the waterbowl size becomes less relevant.
dr del