MIMF

I have an acoustic guitar in the shop that is playing flat on the 12th fret, on the E, A, and D, strings. The others are OK.
I re-shaped the saddle so that the strings are coming off the front of the saddle, and it is still not enough compensation.

My next line of attack is moving the saddle forward on the bass side, but not a lot. I'm thinking 1/16, should do it.
There are two lines of thought going on in my head right now.

1. Simply widen the saddle slot forward, and install a thicker saddle that can be carved so that the affected strings come off the front edge, which would now have been moved forward.
2. Fill the slot, and rout a new one. This presents all the fill in issues. Matching the wood for one. Making the plug secondly. The repair would be visible thirdly.

I am leaning toward the first option, as it is a bit simpler. My problem is this.
The under saddle pickup strip is very close to being as wide as the current saddle. If I widen the slot, and saddle, how does this affect the pickup strip?

Before surgery, make sure the nut is appropriate. If the the nut is too close to the first fret, you will get the symptoms you report. Put capo on the first fret and rerun your tests with the 13th as the new 12th fret.

Otherwise, if you thin the saddle so it will lean, will it lean enough to solve the problem? Beyond that, when I've had to fill and recut a saddle slot, the fill has been practically invisible on rosewood or ebony bridges. I find a piece in the scrap pile that matches and gradually sand it into fit leaving it proud on top to be sanded down later. I use hot hide glue and wait overnight before sanding the protruding top part to match the bridge. If you've never done it before, you can gain confidence by cutting a slot in a scrap piece and filling that before you try the bridge on the guitar. If you can make a bone saddle, you can make a wooden one--that's all the fill piece is.

Thanks Bob. That is what I did. The glue on the fill piece is drying right now.
I'll cut the new saddle slot tomorrow.