Thanks for the update, but the advanced timing tweaker seems buggy for me. This was all tested on Dreamcast RGBHV with the DTV 480P setting.
I assume that the DC aspect fix was supposed to stretch out the image a bit, but all that the H. active setting does for me replicate the left side of the screen and slide it in on the right side as I lower the value. All other settings were left at their defaults for this.
Another issue unless I’m misunderstanding something, if you take H. backporch and lower it some to move the image to the left and then decide to shift it back to the right some, the first time you increase the value it continues to shift the image left one more value instead of to the right. A second increase will start making it shift to the right, but there definitely isn’t a 1:1 relationship with the values and the effect here. This behavior happens going both ways and also happens on other advanced timing settings (I didn’t test them all for it).