By pushing the boost button, it ties the starter battery together with the house batteries. The parasitic draw is the same and still there. The only difference is that the starter battery is now providing 1.95 amps of the drain and the house batteries are providing 0.4 amps. This is confirmation that the drain is on the house side of the system.
Like bobndot suggested, watch the current drain as you remove and reinstall each fuse in the distribution panel. If that doesn't help, there may be high amperage loads connected directly to the load side of the disconnect relay causing the drain to investigate.
Good luck
