The Blackstone has a regulator at the unit. The lp source you are using is already regulated so you are correct in your assumption. The regulator on the grill has to go for it to work properly with the regulated source.
It's a common modification and there are threads that explain it here on JOF.
2011- 351RLTS Eagle, MorRyde suspension & pin box, Hughes PWD50 Power Watchdog, TST
2017- F350 6.7 PSD Lariat FX4,SRW, SB,CC
B&W Turnover ball, Andersen Ultimate 3220
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