What is your experience when u cross a Oxheart x Beef tomato.
Do u have examples what shape the F1 will be?

Green Giant has a beefsteak shape and is PL. Golden King of Siberia has an oxheart shape and is RL.

Green Giant x Golden King of Siberia F1 (RL) had an oxheart shape for me in 2017 (that's how I knew Golden King of Siberia was the father, since I didn't grow any other oxhearts in 2015 when I grew Green Giant and saved the seeds that I grew in 2017, which turned out to be the hybrid).