Hi Robin,
the default can be set in IMG via
Financial Supply Chain Management
Treasury and Risk Management
Basic Functions
Market Data Management
Master Data
Settings for Ref. Interest Rates and Yield Curves
in 'Define Reference Interest Rate' -> Detail screen -> Fixing period.
The 'standard' setting for the 1105 flow is not relevant for posting, yes, but of course this depends on your customizing.
Concerning the payment details from TBI1: this is hard to tell without checking it more closely.
There are currently no known errors and it works in our reference system, so maybe you should check TBI1 again and try with a new deal.
Best regards,
Marie
PS: Please make sure that you create one thread per issue in the future for a better overview.