Although I'm no expert,I can pass on to you my own experiences........
First,it sounds like you're playing on a "Christmas tree" pattern. Oil in the middle with lighter oil to the outside.It also sounds like you're playing where most people with medium revs and ball speed would,and should,play the lanes.Let the oil help your ball clear the head then use the light oil to bring the ball into the pocket.
One thing that you should do is to watch the other bowlers on your pair.Where are they playing?If there are more than one or two on a similar line to your preferred line,your line will disappear quickly,and carrydown will appear.
Second thing is to watch what they're throwing.Pearl stuff or dull??Pearl will push the oil a little farther down,creating a hold area and allowing your line to stay there a little longer before you must move.If this is happening,stay there,but watch the pins as well as the ball.Half tens are telling you to be a little more direct,where 4,9,or solid 7 pins are telling you to move in.
Dull will kill the line quicker and force you to move inside faster.Again,watch the reaction of both ball and pins and adjust by moving inside or go to a less aggressive ball.
By the way,you've only mentioned two pretty strong balls.What's in your bag that's a medium condition ball???I try to start with something medium as a benchmark ball and then adjust as the night goes on
Again,I'm no expert in any way,and don't claim to be.This is simply observations I've made,seen and done in my own game.I really hope this helps you.Keep us posted.......
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Chris
Lane#1--nothing else hits like 'em.