Taking cuttings with a heel?

I am about to take some Erisimum cuttings & like pinks & others I have read or asked about, instructions are to pull off the plant so it has a bit of a heel, some actually say leaving the heel intact.

Most instructions then tell you to trim the botttom. How much do you take off,  do you want any of the heel left, surely I'm going to lose it if I trim it square.....

Sorry if it's a daft question but I'm not very experienced at cuttings & it would be good if someone could clarify which bit is important.

The "heel" will usually end in a long wispy bit, usually of bark with no inner wood showing. That's the bit you can shorten to tidy it up.

Ah, so I'm just trimming the extremity of the heel. That explains it. 

Thank you! 

It's the thin end which is most likely to rot; it's just the tip which needs trimming off.