Jetprosofstretch hasn't cracked in my experience and I've been using it since it came out. While it does stretch with cotton and cotton blends, I haven't used it on a ribbed like this one.
I know of another member who does this as well and says it is no problem this way. They say lower the upper platen and stretch the shirt. (?) Is that how you do this? Just curious, I'm a bit too nervous of ribbing for the same reason the OP is saying, but would like to know what real possibilities are out there that I may use if I need to.When I do tanks that are or anyother strechy material with heat transfers I stetch the shirt on the heat press and keep it stetched untill done. and have had very little problems with cracking and braking.