Matty, the input on an Ion doesn't change according to whether it's HP or LP - the main reg steps it down to 175 psi anyway, so whether its a LP bottle outputting at 400 or a HP at 800, it really doesn't make a lot of difference
Your prob is due to SP shipping Ions with the main reg (therefore velocity) set far too high, which is a cock up, not it being set for LP
It's quite common - and annoying!