Hi Snodger,
I do not think it matters what knot you tie in a leader of 60LB or 80LB it will catch on the guides. I have shortened up my leaders to 18 inches or less and casting the knot from outside the guides. Makes no difference that i can see to the Barra. Many of the pro guides use this method.
As an alternative tie a double to the braid and use a Yucatan knot which is very slim. Another option worth a try would be converting to wind on leaders.
Although some frown upon the use of glues to the knot i will take any advantage i can. There are several options here the cheapest being super glue and the best a product called "knot sense" which coats the knot in a smooth layer of a plastic like substance. Mainly used for game fishing to avoid knot bubbles in trolled skirts and the like. The smooth finish makes the knot bulkier but quite smooth and rounded. It is available from wellsys tackle who have an on-line store.
Good luck with it all