I would say you need compression releases if you don't already have them. Makes life alot easier on the starter. In the meantime, try cracking the throttle a tad bit while starting it, see if that helps alleviate some of the compression.
I've got a 113" in my Fatboy thats at 10.2:1, using the stock starter. As long as I use the compression releases, it turns over with no issues.
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2015 Denim Black RG, FM ss ceramic coated 2-1-2 pipe, White Bros Original E Series Mufflers, FM ac, PV Tuner