Where you hit the ball matters- years ago they had a target on them..
Be carefull though the one in Sports cafe in brum has a chip out of the back plate of it and my knuckle has only really just recovered- 3 and half months later
Low to mid 900's is usually a good score... higher than that I've not seen.
Technique is important- I've seen big lads take run ups and all sorts... but I preffer to do a 1 step then punch and with a few quids you can get power and accuracy without looking like a tit when you floor yourself on the wall behind the machine.