It's quite normal for this to be needing a higher dose than the original to accomplish anything, as the benzodioxol ring has to be opened by metabolism for it to ressemble U-47700 binding-wise.
I think the active form of this (if you overlay structure with morphine) would be the 3,4-(DiHydroxy-Deschloro)-U47700; 3-Ethoxy-4-Hydroxy-DesCl-U-47700 would ressemble EthylMorphine and 3-Hydroxy-4-Ethoxy has it ressemble Morphine (when overlayed). So the closed ring structure allows it to better pass the BBB, but should be less active than it's metabolites as it doesn't ressemble morphine's structure.
Another reason for it to be less potent is that a part of the dose might first be metabolized by N-DiMethylation which renders it inactive before ring-opening.
Just as for codeine and it's derivatives, things like DPH or white grapefruit should potentiate enzymes catalyzing the ring-opening making it more potent (I suppose), and co-administration with BBB passing anti-oxidants should also potentiate it/ make it last longer. (All pure speculation ofc)