To smooth out the tip overlays (or any overlays for that matter) my process is as follows. It took me a while to get to get this down and it used to take me about 45 minutes to do this. With some practice, you can really reduce the work and time. After the overlays are glued on this takes me very little time now.
1. Glue on the overlays with smooth on (except no substitute here as nothing sands better than smooth on). No need to taper the overlays first. Make sure and tape off your limb so you do not get smooth on everywhere.
2. No need to sand off the sides perfectly, leave them a bit wide. Tape off the limb right beneeth the overlay. Use 3 pieces of tape thick.
3. Over to the spindle sander and start to make the transition. Once you get through one piece of tape you know you are close. 180 or 220 grit will work fine.
4. With the tape still on, take your random orbit sander and smooth it out a bit more, eating into one more layer of tape. Try to keep the pressure straight down, right in the middle of the limb, right where you need it so you dont divot the sides of the limb.
5. Take all the tape off except the last piece, hand sand with a small piece of sandpaper...150 or 180 grit and start making the transition. Again, dont round the corners. You will start eating through the last piece of tape. At that point, take the tape off and use 220 to finish the job. The final 220 should only take maybe 5-6 strokes to finish it and done be afraid to stratch the surface of your glass with this 220.
6. After it is smooth with no transition to feel, I always drop a small amount of superglue on the fade, wipe it in. Now sand the sides to the limb.
Note, these pictures are not all of the steps, specifically steps 4 & 5 are not pictures, but I tried to find as many as I could to show the process.