Can't balance arm with Tecnoweight

I have a Rega P25 with an RB600 tonearm. I recently upgraded my cartridge and counterweight. The cartridge is a Benz Ace LOMC. It weighs 8.8g. When I put the Tecnoweight on the end stub, I can't move the weight back far enough to balance the arm.

The directions say that I have to get the arm to balance (or float) just above the record before dialing in my tracking force. But again, I can't. I'm using the heavier of the two weights, but it's not heavy enough to accomplish this task.

I am able to obtain the proper tracking force using my shure gauge, but I can't help thinking that I must be doing something wrong.

Has anyone else experienced this? Is it normal?
Whatever the VTF is at the gauge is really all that matters. Doesn't the Technoweight have several different dials for setting the VTF? I've only setup one before and seem to remember this?
Here's a link to how to install the Technoweight. Looks like you set the Rega's spring loaded VTF to 3.5 grams. Maybe this will help you get it to balance.
I set set the dial at 3.5, so that's not the issue.

I keep wondering if my cartridge is installed properly. I set it up using the single-point rega protractor, and it sits about 1mm beyond the arm. I thought that that extra weight out front could be the reason for my problem. But I've double checked it several times, and it seems to be installed correctly.

In the end, as you mention, Mofimadness, all that matters is the final VTF. But, again, I wonder if my inability to balance the arm is symptomatic of another problem.
I had the same trouble with a rega RB 250 which is supposed to be the ideal arm for it. I found the solution after contacting them. The weight shall be pushed off-center towards the back. I am not native English so I hope my expression is understandable. You can move the weight back for a max of 8mm off the center. Solved now?
I understand what you mean Ad. What's more, I just moved the weight back on the slide tube, as you suggested, and could balance the arm. So this is good news. Although I must admit that I still don't know why it wouldn't balance properly when the weight was attached to the center of the slide tube as the directions say.

Thanks for your help, everyone.