When electing to round up on the cap size, if your post size falls between sizes on the quarter inch increments, you can use the sizing tape, it centers the cap on the post top and acheives a snugger fit before securing in place with an adhesive.
3M™ Performance Plus Duct Tape 8979 has a unique tape construction that allows for both permanent and temporary applications indoor and outdoor. It is removable with little or no adhesive residue from most opaque surfaces up to 6 months after application. The backing is also UV and water resistant.
Click here to view photo of applying sizing tape for a snug fit.
Depending on the style of caps you are fitting, the Sedona with a 1" drop from the top or the Tiara with a 2" drop from the top, mark down from the post top - just a little short of either the 1" or 2 inches, with a scribe or pencil mark.
Now wrap the sizing tape around the diameter of the log, just above the mark, so the blue tape does not show, when the cap is placed down into position on your log top.
How many times you will need to wrap around, depends on how much space is in between the log post sides and cap. Patience attains the goal here, maybe only 1 or 2 times will do it. After you attain the desired fit, apply the adhesive either on the inside of the cap or the log post top and place the cap down on your post.