I'm using Juicy8 (latest build) with Touch InCall Screen Tweak.

My screen doesn't turn itself off while in a call unless the tweak program toggles it off. When I hold the phone face up, the screen comes on and allows me to dial whatever I need, when I told it back up to my face, the screen turns off for me.

So I guess I'm not running into the same problem you are. Give the program a shot, maybe you'll like it.