To achieve maximum possible usage of upper memory blocks (UMBs) for MS-DOS 5.0 or later, set hardware buffers to be contiguous and as low as possible within the C000-F000 range.
By making sure that the address ranges (ROM and RAM) are as contiguous as possible, you will be able to create the largest single, free address range. This will provide more UMBs for MS-DOS than fragmenting the address ranges.
On PC/AT computers, refer to the hardware and software manuals that came with your adapters to determine the address ranges that can be set. Usually, this is done with jumpers on the adapter, but occasionally it must be changed with a setup program. Once you have determined the address ranges, arrange them to be as close together as possible without overlapping.
On PS/2 computers, you will need to run the reference disk and supply the ADF files (if they are not already on the disk) for all the adapters. Using the reference disk program, you can determine address ranges for each adapter, and then set them.