How do you set the percent or amount under the buybox? Now you can only be plus or minus 1%. I want to be able to undercut the buybox by more than 1%. How can I do this now?

That feature is still available, just not the most apparent. 

Go to strategies and edit a strategy you don't need. For example: follow BB +1%.

Then change the values to "subtract this amount" from the best price, change it to the value you want, and then (if you can) rename the strategy.