Need help setting starter on 400 sbc

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I have a new high torque mini starter for my built 400, and i am having trouble setting the clearances. My bendix gear to flexplate clearance is fine, but I am having to install shims between the starter head and the block (obviously), but I have gone up to 1/8th in. in shims and the starter bendix engages the flywheel sometimes, but not everytime I crank. I am not starting the motor when I do this, just simply bumping the starter to see if it engages. Sometimes it will engage two or three times, then the fourth bump the bendix just grinds on the flywheel. I am afraid if I shim it any further away from the block my backlash on the teeth may be too much. I am almost positive the starter should be able to engage any time you crank it, whether the engine has started or not..? Any help is appreciated.
Thanks, Dusty