Anybody add pre shave oil to their soaps??/ how much?

Also, I have some samples from Whipped dog, wondering do you shave chunks off and squish them into a bowl or cup or do you use the whole sample?
I tried shaving some off of one sample and don't think I used enough as I couldn't get it stuck to the bottom of my mug, any tips or tricks?
I have 4 soaps in rotation, but they are the cheaper variety and am wondering how these sample higher end soaps work?

thanks a bunch folks!