Lowbass
Thanks for the information! 
I'll try to give you some help, but I won't be able to
do much until I can get more info. Since you appear to know
Prataman, he should be able to correct any wrong assumptions I
make. 
In such medium conditions, if i polish up with ER, it will give
me lenght, but the backend is somewhat tame.
From your layout, I would say that that drilling is very strong.
As long as the MB is in the strong position, the ball is going to
flare a lot. And since your pin is 3 3/8" from the PAP, that means
you are not going to get the necessary length. A balance hole means
you have the maximum side weight. Basically, your ball is drilled
to hook without much length.
If you do not want to change the layout, here are other things you
can address.
Shining the cover is a very good step. For the medium condition you
described, I had correctly assumed that you play a deep inside line
because the problem you have is very common: playing the wrong
line.
Your ball has length so that means it has energy left. But the flat
hits tell me that you are playing the wrong line. Many people
prefer the inside line because it looks better and less punishing
if missing right of the target than an outside line. In your case,
I think you do not have enough "bite" for the ball to drive through
the pocket, even though the ball has energy left in it. If you
leave a lot of pin 2s and weak pin 10s, this is your problem.
So just adjust to a tighter line, and the carry should
improve.
The problem could also lie with your drilling. It flares so much
that your ball has hooked out, meaning the core has reached its
stable position and will no longer keep the ball moving left. Since
you have trouble playing the ball's surface without the polish on
this condition, I think you also have a lack of speed.
in slight heavier condition, i will "sand" down the ER with
scotchbrite. it will "bite" the lane well, but backend tends to be
a tad too stong.
This hints two things to me. 1) You do not have enough
ballspeed; 2) This combined with your problem on medium conditions
make me believe you have a late thumb release.
1) If your ball is biting but overhooking the pocket, I think you
lack the speed for such an aggressive biting ball. Of course it
could also mean you are playing in reverse block conditions, but
Singapore alleys rarely lay out that condition, so i doubt
it.
2) A stuck or late thumb would lose a lot of length in the shot, as
well as revolutions. In the case of the medium condition, a late
thumb means you do not catch the ball as well, so it slides all the
way past the proper breakpoint. In heavy oil, you are losing length
which causes you to come in too high.
All this is pure extropolation from my room 
, so please do not take it too seriously if they do
not apply to you. Instead, please correct me so that I can be a
better bowler too.
We learn from one another! 
