That's real close. The plastic straw around the bolt fits so closely that it only extends to the top of the tee nut. You want the tee nut entirely encapsulated in epoxy. I found a model at home depot that had 4 prongs on the base, intended to pierce into wood. A little grease is applied to the bolt threads and the bolt threaded all the way to the bottom of the nut, so epoxy doesn't flow into the threads. I put the nut about in the middle of the stem clamping area. Depending on the type of top cap used, you may want to stop the epoxy 2-3mm below the top of the tube. Some top caps have recessed bolts that take up space below the top of the stem.

I used a piece of 1 inch copper tubing with the end sharpened to cut foam rubber. You could also use a 1" copper tube coupling that's a little larger. The bottom has to be sealed, so the epoxy doesn't leak out.

The inside of the steerer should be cleaned with acetone and lightly sanded, with something around 120 grit, then cleaned again with acetone.

To extend a steerer, a 1" no-stop copper tube coupling that as a 1-1/8" inside diameter is slipped over the steering tube and the epoxy extends up to 15mm above the top of the steering tube. The coupling has to be very lightly greased, so the epoxy does not adhere to it. I want more the half of the stem clamping area to be the original steering tube.