So in other words: a non-naval SMR which doesn't use HEU is going to be substantially larger - which would make it substantially more expensive, and therefore not representative of civilian SMRs?
Who said anything about expense? Why does "bigger" equal "more expensive?" Lead, concrete, etc. are cheap on land, but volume is a precious resource on a ship. HEU isn't the only reactor fuel out there, either.
And of course, all non-naval reactors are naturally going to be larger: they aren't surrounded by a practically-infinite fluid heatsink.