My sense is that blocking preflop is primarily a matter of: (i) avoiding opens [or making 3bets (or 4bets)] that we have to fold to reraises; and (ii) making it more likely that our opponents have to fold to our 3bets.

For (i), we open weaker Axxx hands partly because it makes aces less likely, and we 3bet AKKx partly for the same reason.
For (ii), we prefer to 3bet hands that unblock kings--other things equal--since our opponents are supposed to fold most KKxx combos to 3bets.

No doubt I'm missing some, but I think that opening Axxx because it blocks our opponents' calls (as opposed to 3bets) is not a thing. Perhaps there are too many starting hands, even playable hands, in PLO for this to be effective.

Not sure I have much to offer on the issue of Axxx hands to cut out of your UTG opening range. But, as I'm sure you know, the solver is expecting to win the blinds about half the time when opening UTG, and nothing remotely close to this happens in any games that I'm aware of.

If you're playing microstakes where multiway pots are exceedingly common then my advice is this: If you think your Axxx is even close to being a fold, fold it. Playing OOP in MW pots with anything but truly premium holdings is a thankless (and usually profitless) task.

Hope this helps.