I would suspect the flow rate isn't sufficient to get ahead of the leakage.Things you might check are if the spoilboard has a clean seating on the machine,leaks in the plumbing,blockage in the filters and pipes and the presence of holes in the spoilboard.I have known people to varnish or shellac the edges of the MDF to reduce leakage too.If the table has a zoned vacuum grid and you have a gauge,could you determine the level of vacuum in each zone?You could then compare it with the vacuum at t he pump to see if any one branch has a leak.The spec of the pump indicates that it ought to deliver a high enough level of vacuum and if it is meeting that figure at the outlet,the problem is leakage or insufficient capacity.For most machines,flow volume is more important than absolute vacuum,in fact there are lots of machines with a vacuum relief valve in the system.You almost certainly won't be able to listen for leaks if the pump is inside the building as the things are so noisy.