Well, I don't really math; but the way I understand it, computable universe theory suggests Solomonoff's Universal prior, while the ZFC-based mathematical universe theory--being a superset of the computable--suggests a larger prior; thus weirder anthropic expectations. Unless you need to be computable to be a conscious observer, in which case we're back to SI.

The two usual implied prior taken from Level IV are a)that every possible universe is equally likely and b)that universe are likely in direct proportion to the simplicity of their description. Some attempts have been made to show that the second falls out of the first.