(author here) We cross-tabbed system age vs perception of amount of TD. There was a moderate association between older systems (> 6 yrs) and more perceived debt.

I did not explicitly look at size as this was not one of the original research questions, but a good point. I suspect older systems will tend to be larger (in the domains we studied, anyway). And your point about arch choices being great "early on" can, I think, be captured in the "system age" variable. I guess I'm trying to think of a system that might be young and yet quite large in LOC.. would be an interesting outlier to look at.