In AD 30, most all blocking-stones were square/rectangular.1 The presumption then is that Jesus's blocking stone was as well.2
An angel reportedly sat on the blocking stone. This is relevant because wheel-shaped stones typically rolled back in a way that left little room for sitting.1
The stone sealing Jesus's tomb was “rolled” out of the way.1 This is relevant because only a disc-shaped blocking stone could be “rolled.”
But so what? Square blocking stones were rolled as well.2