Yes without a doubt it matters massively a reduction of this much, it's a serious no no, the pumps have ZERO suction, so if flow can't keep up when flat out, they can't suck, your engine could just run lean and melt the pistons etc.
OPA is cheap enough, about £1.50 a foot, so not worth the risk.
Yes sitting empty can kill the pumps, why not check the rail pressure with a gauge, if need be power the pump manually from a battery/jump pack etc.
tabetha