Use 5/8ths. Safer, if your using gear that better god damn not be 'too long'. They sell at WalMart OTC cheap as hell.
1ml 5/8ths Slins, with no backstop so super easy to backload. I think $11 or so for 100.
Shallow injections are nice for recovery, but you will hit an SC layer , sterile abcess from a shakey injection or a pocket of adipose tissue eventually and you will hate your life for atleast week. Also not that anyone gives a shit about 'vector physics' but as you decrease the length of the pin even a tiny increment, the probability of pinning in the exact same spot (generally bad news) is markedly increased.
I know 1/2 - 5/8ths is pretty negligible, but it wasnt more than a year or two ago that most people wouldn't recommend anything less that 1' for an oil injections.