Yes ‘ian s’ you are quite right, except I am using eighth triplets not eights.
As an experiment, I changed the signature to 12/8 and indeed 11/8 was available, however, this requires me to edit the drum and bass parts as the notes are the wrong length. The tempo also needs to be changed from 110 bpm to 165 bpm to resynchronise my audio tracks. Very interesting.
I just find it ‘odd’ (pun intended) that you can’t select a 1/8T as a signature base.
Because */*T is not a time signature! The way in which notation works is that */4 or */2 denotes (ouch!) a duple pulse base and */8 denotes a triple pulse base. The 8 as the denominator in the time signature has nothing to do with 8th notes - it indicates triplet pulse. Unfortunately the way you’ve transcribed your parts would appear to be, in musical notation terms, grammatically incorrect even though mathematically the structure you have used adds up. if you have a part with a predominantly triple pulse, adopting a */8 time signature from the start will avoid you having to re-edit the parts.
Meanwhile, the thread that Steve quotes above has detailed info on to get your current piece into the right time signature/ tempo framework