I think you may need to be browsing Bicester records, the images are online. I have not looked further back than this baptism for Thomas.
I have now looked at the original and the letter taken as 'o' is the same as the presumed 'e' in Potter, Turner and Baptized on that page and in that case is definitely Keen and not Roon so most likely your Thomas Keen. There are other examples of transcription errors in Bicester for Keen around the same time with father Thomas.
Marriage at Bicester 6 May 1759
Thomas Keen and Sarah Archer
An Isaac Archer was one of the witnesses