as far as I'm aware the rba won't fit. The supplied coils are the ones with the narrow top same as the gtx18 coils and the rba is the same size as the wider top coils that won't fit the gtx18.
a suggestion for
@Vaporesso to pass on is to rename the gtx coils as something like gtx-a for the wider topped coils including the rba and gtx-b for the narrow topped coils.
This will save confusion. as when people see compatible with gtx coil range, like me they think compatible with the whole range. not compatible with some of the range.