12-15 is too oily? that is odd.
Usually a reverse block is not put out much, if at all any more. True Flat oil, like at the PBA Open, is hard enough and plays like a reverse block.
Normal attack is to to play 4th/5th/6th arrow, depending on the ball you use and your release strength, targeting a breakpoint of 12-15, again depending on the actual pattern.
Now if it's oily outside 6, but less oily between 7 and 11, with a lot of oil between 12 & 15, that sounds more like just a messed up shot.
If it's less oily between 7 & 11, try a medium strong, decent surface for your release and ball speed ball and target that as a brekapoint.
This doesn't sounds like either a reverse block or a flat oil pattern.
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