Ray, that's plenty of BH. I have the exact same issues with my Osage longbow, I think it's just a characteristic of longbows. Form could reduce some of it, but if you are going to shoot a longbow then the armguard will always be necessary equipment.
When I shoot my recurve that's shorter, more brace height and a bit quicker, I don't even have to wear an armguard and I shoot in a sleevless T-shirt most of the time. I have yet to slap my arm with it.
The longbow on the other hand slaps me about every other shot and I have to wear an armguard.
When I first finished the bow and shot it, I didn't have the exact string that I needed and made due with one that I made and it didn't fit exactly perfect and it also had some stretch to it. When my new Flemish twist string finally came in my brace height increased to where it should be at 7" on a 68" longbow, I now get less slapage and it's more accurate. It's actually more brace height than I expected, but it has only helped my groups so I ain't complaining.