that generally happens when youre air tansk not in properly adn on/off drop forward soon sorts that outits to do with recharge and drop off, if you have a higher input pressure then you are less likely to suffer drop off if your reg isnt recharging quickly enough (because there is more pressure there already).
its a kind of cushion if that makes sense
ive run lp on many markers and never had a problem but HP is recommended as already said