Yes, it's always an interesting topic!
I was advised that the deeper & closer to the internal muscle, the more effective.
I don't know for sure, but I know I was able to use this method and insert my finger to under the first knuckle.
The effects of Diltiazem seemed to be really effective in reducing pain levels & spasms for me, which allowed me to go on and heal a few months later. I also used probably a little more than a pea-sized amount each time & didn't develop any other issues.

I seem to be getting a burning sensation about 1-2 hours after applying the cream. Could it be Diltiazem or something else? Any way to combat that burning? I don't want to stop using the cream.

It only takes a few cm to reach the internal sphincter, and that's where its supposed to go :-)

I just got the prescription today and I was told to apply it around the ring and just barely inside. Definitely not as deep as I could go.

I think ill just use a Qtip for application.

Hazzaal, you do not need to insert anything inside. As far as I am concerned, doing this simply risks doing more damage to the area.

My CRS advised me to apply it only on the outside. I don't claim this is the right way or the best way, but that's what I was told.