As reported by Mother Jones, Rand Paul has been making some rather unusual statements regarding Reagan's domestic spending record.  Paul went on record with the following quotes in various speeches:

Domestic spending went up at a greater clip under Reagan than it did under Carter.

During Reagan's two terms, domestic spending went up faster than Jimmy Carter.

We live in such bad times that if you don't have somebody who truly believes that we need to take an ax to government, you're not going to get anything done ... Even when we elected Reagan. A lot of us loved the rhetoric of Reagan. My dad supported Reagan in 1976 when only four US congressmen would stand up for him. The deficit still exploded ... The deficit exploded because domestic spending rose faster under Reagan, so did military, but domestic spending rose faster under Reagan than under Jimmy Carter ... We have to admit our failings because we're not going to get new people unless we become believable as a party again.

While Vox.com did note the errors in these statements, their analysis of the domestic (i.e., non-defense) spending records of Reagan versus Carter focused on the irrelevant non-inflation-adjusted nominal total domestic spending growth between the two presidents, as well as the less useful total domestic spending as a percentage of GDP records of Carter, Reagan, and the other presidents since.

Total spending isn't of interest, particularly in nominal terms.  If you aren't correcting for both population growth and inflation, the data is nonsense.  And a real measure of fiscal conservatism is per-capita spending in real dollars, rather than just normalized to the size of the economy.

And on this most rigorous fiscal conservatism platform, obtained by calculating the average annual change in per-capita total non-defense spending over each president's term(s), Reagan is the best-performing president since World War II.

During Reagan's eight years in office, real per-capita domestic spending increased 6.1 percent.  For Clinton, the increase was 6.8 percent.  In contrast, Carter increased spending 14 percent in only four years.