Barge board / fascias

[23vc]

Am I right in thinking the barge board has to be less deep than the fascia, in order for the box section to work?
I've used 175mm fascias, and was planning on using the same for barge boards, but I think the plumb cut of the barge board will be deeper than the fascia so it won't work? In which case I can hopefully use a 150mm barge board?
Or I may have totally misunderstood, any info appreciated!

 

[23vc]

Just realised that I'm talking bollards, and that's the whole point in having the eaves box section to get around this issue and avoid a direct join between fascia and barge board .... I think