1 inch will be fine.
Back in the early 1990's some studs were coming with the threads too long. When installed they would bottom in the hole, leaving threads above the deck. Seen several of them snap at that thread. Spent a bunch of time shortening the threads and then spot facing the head because the O.A. length was too short.
I would double check how much actual thread engagement you have with those bolts. Looks like it may be pulling on the top threads. As for how long the engagement should be, you'll have to look at a stock bolt and make sure from under the head to the start of the threads is correct.
