In a multicell setup there are several "Base station settings" that can be changed, but the documentation is very sparse about the actutal implications of those settings:
Number of SIP accounts before distribution load: I know what it means, but what are "good" values for a given setup? I guess it depends on Base station density, handset density and the average number of concurrent calls, but who knows?
SIP server support for multiple registrations per account: Like before, I know what this means (techincally). But what are the advantages of enabling or disabling it?
As far as I understood your system, the handset performs the SIP registeration from one of the base stations, and remains registered on that base station even if it roams to a different base station. Is it possible to detect on which base station a handset is currently connected (DECT-wise, not SIP)?
To try and answer your questions,
Number of SIP accounts before distribution load
This setting provides for call distribution and load balancing across the Multicell based on factors such as load, capacity and available resources. A single Base can have up to 30 handsets, but there is a limitation on concurrent calls. If users are experiencing a call blockage issue as a result of no available channels for calls, this setting may be useful (See Step#2 and #3 of the DECT Multicell Deployment Guide) https://service.snom.com/display/wiki/DECT+-+1.+Multicell+Deployment+Guide
SIP server support for multiple registrations per account
This setting (enabled or disabled) is used for purposes of handsets roaming from DECT bases to DECT base in a Multicell. Here is an explanation of this setting;
You should be able to determine which handset the base is registered to (SIP) in the Extensions page of the M700 if network_roaming_deregister is enabled and if it is disabled, then the SIP registration will exist on its primary base and the base that it roams to.
I hope this answered your questions.