The /storage/.smb/smb.conf location is not used anywhere in modern versions of LE .. use /storage/.config/samba.conf (rename the sample conf) and set the following values (notice they are uncommented):
# The following are default values for the master selection process
local master = no
preferred master = no
domain master = no
os level = 100
reboot to make the new config active; if /storage/.config/samba.conf exists it is used in preference to the embedded one.
This will not prevent one of the LE devices from being elected master in the event you turn off the server master browser; the system works to always have one elected master. However, with that config and the high oslevel value (lowest is better in an election) the LE devices should conceed the election to the server quickly when it reappears, although quickly is not a word that should be used here.